The Project Gutenberg eBook of Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, Second Part: Subclass Osculosa; Index, by Ernst Haeckel

Report on the Radiolaria collected by H.M.S. Challenger during the years
1873-1876.

Legion III. NASSELLARIA,

Nassellaria (inclusis Spyridinis), Ehrenberg, 1875.

Monopylea, Hertwig, 1879.

Monopylaria, Haeckel, 1881.

Cyrtida et Acanthodesmida, Haeckel, 1862.

Cricoidea, Bütschli, 1882 (L. N. 40, p. 537) = Nassellaria.

Definition.—Radiolaria with simple membrane of the central capsule, which is monaxon or bilateral, and bears on one pole of the main axis a porous area (porochora), forming the base of a peculiar intracapsular cone (podoconus). Extracapsulum without phæodium. Skeleton siliceous, very rarely wanting. Fundamental form originally monaxon, often dipleuric or bilateral.

The legion Nassellaria vel Monopylea, in the extent here defined, was constituted in 1879 by Richard Hertwig in his work Der Organismus der Radiolarien (pp. 133-137). He gave to this large group the rank of an order, and united in it the two families Acanthodesmida and Cyrtida, which I had constituted first in 1862 in my Monograph (pp. 237, 265, 272); but he added, too, as a third family the Plagiacanthida, united by me with the former. In the first system of Ehrenberg (1847, loc. cit., pp. 53, 54), four families belonging to the Monopylea were enumerated, the Halicalyptrina, Lithochytrina, Eucyrtidina, and Spyridina. He united the three former under the name "Polycystina solitaria," which he afterwards changed into Nassellaria (1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 157).

In my Monograph of the Radiolaria (1862, pp. 265-345) forty-four genera of Nassellaria were enumerated (six Acanthodesmida and thirty-eight Cyrtida), whilst the total number of genera in the whole class of Radiolaria at that time amounted to one hundred and thirteen. But owing to the astonishing number of new and interesting forms of this legion which I afterwards detected in the collection of the Challenger, in 1881 I distinguished in my Prodromus not less than three hundred and seventeen genera. These were disposed in five large main groups, retained in the present Report, with twenty-six families, viz., (1) Plectoidea (with three families), (2) Stephoidea (with four families), (3) Spyroidea (with four families), (4) Botryodea (with three families), and (5) Cyrtoidea (with twelve families). The first two groups have an incomplete or rudimentary skeleton, and may be united in the order Plectellaria, whilst the other three families possess a complete latticed shell, and {890}may be united as Cyrtellaria. The former correspond to the Acanthodesmida, the latter to the Cyrtida in my Monograph.

The character common to all Monopylea or Nassellaria, which separates them from all other Radiolaria, was first recognised by Richard Hertwig in 1879, and consists in the singular structure of the monaxonian central capsule, bearing on the basal pole a peculiar porous area or operculum, the "Porenfeld;" we call it shortly the "porochora." It represents a circular or elliptical porous plate on the basal pole of the vertical main axis of the central capsule, and bears a peculiar "podoconus" or "Pseudopodien-Kegel," a conical body of singular structure, protruding inside the membrane into the capsule. The pseudopodia arising from this peculiar "podoconus" proceed from the capsule piercing the "porochora," whilst the other parts of the capsule are not perforated.

The Monopylea are therefore "Merotrypasta," like the following fourth legion, the Phæodaria or Cannopylea. But in these latter we find on the basal pole of the monaxonian capsule only one single large main opening, prolonged into a peculiar tube, and there is no trace of the typical "podoconus," characteristic of all Nassellaria. The latter agree, however, with the former in the possession of a basal opening, serving for the emission of the pseudopodia, and in the monaxonian fundamental form, arising from this structure. Therefore these two legions of "Merotrypasta" exhibit a wider divergence from the Acantharia and Spumellaria, the two legions of "Holotrypasta," in which the central capsule is everywhere perforated by innumerable small pores (compare above, pp. 5, 6, 716).

The Skeleton in all Nassellaria consists either of pure silica, or of a peculiar silicate; never of acanthin (as in all Acantharia). The siliceous bars and beams constituting it are invariably solid (as also in the Spumellaria); never hollow (as in the Phæodaria). In the small family of Nassellida alone (with the two genera Cystidium and Nassella) the skeleton is entirely absent. In all other genera of Nassellaria the siliceous skeleton is more or less developed; imperfect, or quite rudimentary in the Plectellaria (Plectoidea and Stephoidea), but perfect and forming a regular lattice-shell in the Cyrtellaria (Spyroidea, Botryodea, and Cyrtoidea). The different forms of this skeleton exhibit an extraordinary variety, but may be reduced to a few very simple fundamental forms, or even to a single, most simple original form. The comparative morphology is more interesting, but also more difficult to understand than in any other Radiolaria.

The geometrical fundamental form of the skeleton is in all Nassellaria monaxonial, the vertical main axis of the body, which is already indicated by the axis of the central capsule with two different poles, being also expressed constantly in the form of the skeleton. The lower or basal pole of the latter always exhibits a different shape from that of the upper or apical pole. This difference is so striking in nearly all Monopylea, that the two poles may be determined on the first view.

In the great majority of Nassellaria not only is the monaxonial fundamental form expressed, but also the dipleuric or bilateral, so that the symmetrical halves of the body may be easily determined; the right and left halves exhibit the same symmetry as in the vertebrates, so that we may distinguish an anterior ventral and a posterior dorsal face of the body. The whole form is in this case determined by three dimensive axes, perpendicular to one another, two of which are heteropolar, the third is homœopolar. The apical pole of the vertical main axis (principal or longitudinal axis) is different from the basal pole. The ventral pole of the horizontal sagittal axis (or dorso-ventral axis) is different from the dorsal pole. The right pole of the horizontal transverse axis (lateral or frontal axis) is equal to the left pole. Therefore the sagittal or median plane of the body (in which the principal and the sagittal axis are crossed) divides it into symmetrical equal halves and is perpendicular to the frontal axis.

Three different original elements of structure are recognisable in the majority of Nassellaria, viz., (1) a vertical simple ring, the primary or sagittal ring, placed vertically in the sagittal plane and enclosing the median plane of the central capsule; (2) a basal tripod, composed of three diverging radial rods, which are united on the basal pole of the central capsule and are either expanded horizontally or descend; (3) an ovate or subspherical, simple lattice-shell, the cephalis or capitulum, which surrounds the central capsule and exhibits a peculiar structure on its basal pole.

These three important original elements of structure—the sagittal ring, the basal tripod, and the latticed cephalis—are so united in the majority of Nassellaria that the cephalis rests upon the tripod and includes the sagittal ring wholly or partially. The simplest realisation of this typical union is afforded by the Archiperida and Tripospyrida, and these may be derived from the simpler important Stephanid Cortina (Pl. 83, fig. 9; Pl. 92, fig. 21; Pl. 97, fig. 1). In this and in all other tripodal Nassellaria, the three basal rods or the "cortinar feet" are constantly so arranged that an odd or posterior rod, the "caudal foot" (c) is opposed to the two anterior paired rods, the "pectoral feet" (one right, p″, and one left, p′). The caudal foot lies in the sagittal plane, and is prolonged upwards into the dorsal rod of the sagittal ring (b), and over this in a free ascending spine, the "apical horn" (a). The curved ventral rod of the ring (r) is united above with the base of the apical horn, below with the common centre of the tripod or the "cortinar centrum." The characteristic position of the central capsule in this skeleton of Cortina is such that its basal pole (with the porochora) rests upon the centre of the tripod, whilst its sagittal perimeter is separated from the surrounding ring by the calymma; the numerous pseudopodia arising from its base diverge downwards and are supported and protected by the three basal feet of the tripod (Pl. 97, fig. 1). Compare also Pls. 51, 53, 84, 95, 98.

The typical skeleton of Cortina, a tripodal ring, becomes more developed in the Semantid Cortiniscus, in which the basal parts of the three diverging feet are united {892}by a second horizontal ring, the cortinar or basal ring (Pl. 92, figs. 11-13). The pores between the former and the latter, or the "cortinar pores," may be regarded as the first beginning of the lattice-plate, composing the "cephalis" or the simple primordial shell in the Archiperida and Tripospyrida, and transmitted from these by heredity to the great majority of Nassellaria.

The "cephalis or capitulum" (the "Köpfchen" of the German authors) is therefore the most important part of the skeleton in all Cyrtellaria, or in all Nassellaria possessing a complete lattice-shell. In the Plectellaria, however, or in those Nassellaria which do not possess a complete fenestrated shell, the "cephalis" is either imperfect or totally wanting. The cephalis surrounds the enclosed central capsule on all sides in the form of an ovate or subspherical lattice-shell, and is separated from it only by the jelly-like calymma. The sagittal ring is either enclosed in the wall of the cephalis (whole or partially), separating its two lateral halves, or it is enclosed in the cavity of the cephalis and connected with its sagittal perimeter by short beams. The base of the cephalis (with the cortinar plate) often rests immediately upon the centre of the tripod; in the majority of Nassellaria, however, this near relation is altered by reason of later changes and secondary modifications.

The number of various forms, developed from these simple original structural elements of the skeleton, is astonishing, and there are described more than three hundred genera and nearly two thousand species of this legion in the following pages. This large number may be easily increased by subsequent observers. Since in all these Monopylea the characteristic structure of the central capsule is identical, and also the structural elements of the siliceous skeleton are similar, it is very probable that they may have arisen from a single common stock. But it is very difficult (and at present impossible) to explain a natural monophyletic system of this large legion. The greatest difficulty is presented by the fact that the three structural elements mentioned above, viz., the sagittal ring, the basal tripod, and the latticed cephalis, are not constantly united, but each alone may also constitute the skeleton by itself. In this respect the following seven cases are possible, and are actually realised.

A. The skeleton is composed of the sagittal ring only and of its spiny appendages, without basal tripod and without latticed cephalis. This is the case in the majority of Stephoidea (Stephanida, Semantida, Coronida, and Tympanida).

B. The skeleton is composed of a basal tripod only (Plagiacantha), or of a tripod in the centre of which arises a vertical apical horn (Plagoniscus), and often of an irregular framework, arising from the rods of the tripod; but there is neither a trace of a sagittal ring nor a complete latticed cephalis. This is the case in the remarkable suborder Plectoidea (Plagonida and Plectanida).

C. The skeleton is composed of a latticed cephalis only, a simple ovate or subspherical fenestrated shell, which encloses the monopylean central capsule; there is no {893}trace of a sagittal ring nor of a basal tripod. This is the case in the remarkable family of Cyrtocalpida (Archicorida and Archicapsida), in numerous Botryodea and in other Cyrtellaria.

D. The skeleton is composed of a sagittal ring and a basal tripod, without latticed cephalis. This is the case in a few, but very important forms of Stephoidea: Cortina, Stephanium, Cortiniscus, Stephaniscus, Podocoronis, and some allied genera.

E. The skeleton is composed of a sagittal ring and a latticed cephalis, but without basal tripod. This is the case in numerous Cyrtellaria, in the Circospyrida (or Zygospyrida apoda: Dictyospyris, Circospyris) and some other Spyroidea; and in a large number of Botryodea and Cyrtoidea eradiata (a part of the Sethocyrtida, Theocyrtida, Lithocampida, and others).

F. The shell is composed of a basal tripod and a latticed cephalis, but without any trace of the sagittal ring. This is the case in numerous Cyrtoidea triradiata and multiradiata, and perhaps in the majority of the following families—Tripocalpida, Tripocyrtida, Podocyrtida, and Podocampida.

G. The shell is composed of all three above-mentioned elements, of a sagittal ring, a basal tripod, and a latticed cephalis. This is the case in the great majority of Spyroidea (with a few exceptions only), and perhaps also in the majority of Cyrtoidea.

The survey of these seven groups, A to G, each of which is represented by numerous living forms, shows clearly how difficult and complicated the morphology and phylogeny of the numerous Nassellaria must be. For all possible combinations of the three original structural elements are realised abundantly, and in such complicated relations, and so intermingled in the different orders and families, that it seems nearly hopeless to answer the question of their true origin. The identity in the structure of the central capsule, however, in all these Monopylea, makes it probable that they have all arisen originally from the skeletonless Nassellida (Cystidium, Nassella), either in a monophyletic or in a polyphyletic way. In this respect the following phylogenetical hypotheses are possible.

1. Monophyletic hypothesis, deriving all Nassellaria from a simple sagittal ring (Archicircus, Lithocircus, &c., Pl. 81). The groups A, D, E, and G may be derived easily from such a ring, but the groups B, C, and F only by means of the hypothesis that the original ring may be completely reduced and finally lost. This hypothesis was stated by me in the years 1877 to 1879, when I had got the first general survey of the astonishing number of new Nassellaria in the Challenger collection, and as I had found the sagittal ring in the majority of them. This, my former hypothesis, is mentioned by Richard Hertwig (1879, loc. cit., pp. 68, 126). It was afterwards supported with particular energy by O. Bütschli (1882, Zeitschr. für wiss. Zool., Bd. XXXVI.).

2. Monophyletic hypothesis, deriving all Nassellaria from a basal tripod (Triplagia, Plagoniscus, &c., Pl. 91). The groups B, D, F, and G, all triradiate, may {894}be derived easily from such a tripod; but the groups A, C, and E only by means of the hypothesis that the original tripod may be completely reduced and finally lost. This hypothesis was employed in 1881 in my Prodromus, since I had convinced myself that the "triradial structure" is prevalent in the great majority of Nassellaria, and is perhaps more important than the sagittal ring.

3. Monophyletic hypothesis, deriving all Nassellaria from a latticed cephalis, a simple ovate or subspherical fenestrated shell without ring and tripod (Cyrtocalpis, Archicapsa, &c.). The groups C, E, F, and G may be derived easily from such a cephalis, but the groups A, B, and D only by means of the hypothesis that the sagittal ring as well as the basal tripod may remain as the last remnants of a reduced cephalis. This hypothesis was given in 1862 in my Monograph, where I constructed the first pedigree of Radiolaria (p. 234). I there derived all the Cyrtida from the Sphæroidea (Cyrtidosphæra), supposing that Cyrtocalpis and some other Monocyrtida may form a direct phylogenetical passage from the Sphæroidea to the Cyrtoidea.

4. Polyphyletic hypothesis, deriving the different groups of Nassellaria from different skeletonless Nassellida, by development of simple siliceous skeletons in different ways. Among the numerous polyphyletic hypotheses which are possible, one of the simplest would be the supposition that three different fundamental forms of skeleton may have arisen independently one from another: (1) a simple sagittal ring as original form of the Stephoidea and Spyroidea (A); (2) a simple basal tripod as original form of the Plectoidea (B); (3) a simple latticed cephalis as original form of the Botryodea and Cyrtoidea (C). This triphyletic hypothesis is supported by R. Hertwig (1879, loc. cit., p. 136); he assumes that the original skeletonless Nassellida (Cystidium) have produced three different branches, his "Acanthodesmida" (= Stephoidea and Spyroidea) with a primary ring, his "Plagiacanthida" (= Plectoidea) with a primary tripod, and his Cyrtida (= Botryodea and Cyrtoidea) with a primary cephalis. This hypothesis seems rather probable on the first view; but it meets with the greatest difficulties in view of the fact that these three original elements of the skeleton are more or less evidently combined in the great majority of Nassellaria. The greatest difficulty arises from the fact that often among very similar and closely allied forms the first exhibits all three elements (A, B, C) combined, whilst the second has a combination of A and B, the third of B and C, the fourth of A and C; and there are other forms, very similar to the former, in which one element only is recognisable. Another difficulty arises from the fact that the intimate structure of the cephalis in the majority of Cyrtellaria is not perfectly known, and often exhibits structures which are difficult to explain with regard to the three elements A, B, C. Under these circumstances further researches on the numerous imperfectly known Nassellaria are required, and chiefly accurate observations on their more minute structure and on their important ontogeny.

We divide the immense legion of Nassellaria into two large orders, the Plectellaria without complete lattice-shell, and the Cyrtellaria with a complete lattice-shell or a "cephalis," including the central capsule; the latter, of course, have arisen from the former. The Plectellaria comprise three different suborders, the Nassoidea (without skeleton), the Plectoidea (with a tripodal skeleton, without ring), and the Stephoidea (with a primary sagittal ring, with or without tripod). The Cyrtellaria again also comprise three different suborders, the Spyroidea (with bilocular cephalis and a sagittal constriction), the Botryodea (with multilocular and lobate cephalis, exhibiting two or more constrictions and three or more lobes), and the Cyrtoidea (with simple, unilocular cephalis, without constriction).

Synopsis of the Orders and Suborders of Nassellaria.

Order V. PLECTELLARIA, Haeckel, 1883.

Definition.—Nassellaria without complete lattice-shell, usually with an incomplete skeleton, formed of a ring, a tripod, or an irregular framework.

Suborder I. NASSOIDEA, Haeckel.

Family XLV. Nassellida, Haeckel.

Cystidina, Haeckel, 1883, Sitzungsb. Jena Ges. für Naturw., Februar 16.

Definition.—Nassellaria without skeleton. The soft body composed of a monopylean central capsule (with porochora and podoconus) and of a surrounding jelly-veil or calymma.

The family Nassellida comprises the simplest and most primitive forms of Nassellaria, the only group which is entirely without a skeleton. The central capsule is therefore perfectly free and naked, enveloped by the calymma only, as in the Colloidea among the Spumellaria, in the Phæodinida among the Phæodaria. Probably these naked and skeletonless Monopylea must be regarded as surviving remnants of the common ancestral group of this legion; but the possibility is not excluded that the few observed forms are either young Nassellaria which have not yet secreted a skeleton, or older Nassellaria which have lost their original skeleton.

We distinguish in this small family two genera only: Cystidium with hyaline, not foamy calymma, without extracapsular alveoles, and Nassella, with a very voluminous foamy calymma, including numerous large alveoles; the former corresponds to Actissa and the latter to Thalassicolla among the Colloidea or the skeletonless Spumellaria. But in these two latter genera, as in all Peripylea, the central capsule is perforated everywhere by innumerable small pores; the two former genera, however, exhibit the same characteristic podoconus in the central capsule, and the same porochora at its base, as all the other Monopylea. The pseudopodia are protruded from the central capsule through the porochora only.

The Central Capsule is in the two observed genera either ovate or nearly spherical, usually slightly tapering towards the basal mouth. Its transverse section is constantly circular. The membrane of the capsule is usually rather thick and double-contoured, and bears on the truncate basal pole a circular "porochora" or area porosa, through which the pseudopodia are protruded. The porochora is either quite simple, circular, or in some species trilobed, with three equal circular lobes, each of which is surrounded by a girdle of small granules. The podoconus, or "pseudopodial-cone," arising vertically from the horizontal basal porochora, is half as long as the central capsule, or longer, simply conical and finely striped longitudinally. The nucleus lies usually in the uppermost part of the central capsule, above or behind the podoconus, and is either spherical or ovate, sometimes kidney-shaped. It includes one or more nucleoli.

Synopsis of the Genera of Nassellida.

Genus 382. Cystidium,^[1] R. Hertwig, 1879, Organismus d. Radiol., p. 87.

Definition.—Nassellida with hyaline calymma, without extracapsular alveoles.

The genus Cystidium is the simplest and most primitive among all Nassellaria, and may be regarded as the common ancestral form of this legion, for which it has the same high importance as Actissa for the Spumellaria. The central capsule is quite simple, ovate or nearly spherical, and included in a voluminous hyaline calymma, which contains no large alveoles. Cystidium differs from Actissa, its probable ancestral form, in the possession of the "podoconus" and its basal "porochora," characteristic of all Nassellaria or Monopylea.

Central capsule ovate, one and a third times as long as broad. Podoconus with simple circular porochora, about half as long as the capsule, surrounded at its base by red granules of pigment. Nucleus spherical. Three equal oil-globules in the endoplasm. No pigment in the voluminous calymma, which includes numerous xanthellæ.

Dimensions.—Length of the central capsule 0.1, breadth 0.075; nucleus 0.035.

Central capsule ovate, one and a half times as long as broad. Podoconus with simple circular porochora, three-fourths as long as the capsule. Nucleus ellipsoidal. No oil-globules in the endoplasm. No pigment and no xanthellæ in the calymma.

Cystidium inerme, R. Hertwig, 1879, Organismus d. Radiol., p. 87, Taf. vii. figs. 1-1b.

Central capsule subspherical, a little longer than broad. Podoconus about two-thirds as long as the capsule, with trifid porochora, which is composed of three equal circular lobes. Nucleus spherical. Numerous oil-globules in the endoplasm. The calymma includes numerous xanthellæ and brown pigment around the mouth.

Genus 383. Nassella,^[2] nov. gen.

Definition.—Nassellida with foamy calymma, containing numerous large extracapsular alveoles.

The genus Nassella differs from the preceding Cystidium, its probable ancestral form, in the development of numerous large alveoles in the extracapsular calymma, and therefore exhibits the same relation to it that Thalassicolla bears to Actissa among the Spumellaria. The foamy calymma is very voluminous, and includes numerous symbiotic xanthellæ.

Central capsule spherical. Podoconus with simple circular porochora, half as long as the capsule. Nucleus spherical. Numerous oil-globules in the endoplasm. Calymma spherical, without pigment, with numerous xanthellæ and large alveoles.

Dimensions.—Diameter of the central capsule 0.12, nucleus 0.04, calymma 0.6.

Central capsule ovate. Podoconus two-thirds as long as the capsule, trifid, with three equal circular lobes (as in Cystidium inerme). Nucleus ovate. Three equal large oil-globules in the endoplasm, corresponding to the three lobes of the porochora. Calymma ovate, in the upper half much more voluminous than in the lower, including numerous large alveoli and xanthellæ, and around the mouth masses of black pigment.

Suborder II. PLECTOIDEA, Haeckel.

Plectoidea vel Plectida, Haeckel, 1881, Prodromus, p. 423.

Plagiacanthida (sensu ampliori), R. Hertwig, 1879, Organismus d. Radiol., p. 72.

Definition.—Nassellaria with a rudimentary, originally tripodal skeleton, composed of radial spines, arising from one common central point or central rod; the spines are simple or branched, and the branches may form by concrescence of their meeting ends a loose wickerwork, but never a complete lattice-shell. Never a ring in the skeleton.

The suborder Plectoidea, hitherto known by few species only of "Plagiacanthida," comprises a large number of interesting Nasselaria, which belong partly to the simplest and most primitive forms of this legion. It may be divided into two different families, Plagonida and Plectanida. In the first family, Plagonida, the monopylean central capsule is supported by a simple or rudimentary skeleton, composed only of a variable number of radial spines united in a common centre. In the second family, Plectanida, the branches of these radial spines become united and form a loose irregular framework with wide meshes, partly enclosing the central capsule, but never a perfect lattice-shell.

The Plectoidea differ from the following suborder, the Stephoidea, in the absence of the ring, characteristic of the latter. Some slight traces, however, indicate a near affinity between the ringless Plectoidea and the ring-bearing Stephoidea. Both these suborders of Plectellaria differ from the closely allied Cyrtellaria (Spyroidea, Botryodea, and Cyrtoidea) in the absence of a complete lattice-shell. The morphological relation and phylogenetic affinity between the former and the latter have already been discussed in the preceding description of the legion Nassellaria (compare pp. 891-894).

The first known species of Plectoidea was observed in the North Atlantic (on the Norwegian shore) in 1855 by my late friend Edouard Claparède, and described and figured in his Études, &c. (1858), under the name Plagiacantha arachnoides. He considered it as a new genus of Acanthometrina. Another species, from the Mediterranean, was described in the same year by Johannes Müller as Acanthodesmia dumetum (1858, loc. cit., Taf. i. fig. 3). A third species, also Mediterranean, was figured by me in 1865 under the name Acanthodesmia polybrocha. Finally, Richard Hertwig, 1879, in his Organismus der Radiolarien, gave a very accurate description of another Mediterranean form, Plagiacantha abietina (loc. cit., Taf. vii. fig. 6). He first recognised the true character of Monopylea in their monaxonian central capsule, and observed at the same time the first Nassellarium without skeleton, called by him Cyrtidium inerme (loc. cit., Taf. vii. fig. 1). To these four known species, representing three different genera, the rich collection of the Challenger has added so many new forms that we may distinguish here not less than seventeen genera and sixty-one species. In my Prodromus (1881, p. 423) I arranged these in two subfamilies, the Plagonida and Plectanida, constituting together the family Plectida (identical with the "Plagiacanthida" of Hertwig and Bütschli). But at present, regarding the important relations of these Plectida to the other Nassellaria, it seems more convenient to give to them the rank of an independent suborder of Radiolaria, under the name Plectoidea.

The peculiar structure of the central capsule of the Plectoidea, first recognised by Richard Hertwig, allows no doubt of their being true Monopylea or Nassellaria; and also their siliceous, originally triradiate skeleton indicates the nearest affinity to {900}the other families of this legion. But a very difficult and as yet unsolved problem is the important question, in what manner these different groups of Nasselaria are phylogenetically connected. Either the Plectoidea—as the simplest of all—are the original common ancestral group of this whole legion (as I assumed in my Prodromus, 1881), or they are derived from the Stephoidea (by reduction of the sagittal ring), or they have originated independently from them (if we suppose a polyphyletic origin of the Monopylea. Compare above, p. 893, &c.). In any case the typical "triradial structure" of the Plectoidea, prevalent also in the other groups of this legion, is a very important and interesting fact.

The triradial skeleton of the Plectoidea exhibits in the two families of Plagonida and Plectanida a complete homology of development, so that each genus of the latter may be derived from a corresponding genus of the former, simply arisen by concrescence or union of the branches of the radial spines. Therefore the only difference between the two closely allied families is, that the branches of the radial spines in the Plagonida remain free, whilst in the Plectanida they produce a loose framework or wickerwork by union of their meeting ends. We express this complete homology in the nomenclature of the Plectoidea, in each genus of Plagonida retaining the syllable "Plag-"; in each genus of Plectanida, correspondingly, the syllable "Plect-."

The number of radial spines composing the skeleton is originally three, and in all not triradial genera is probably derived from three. For better survey we may divide each family, according to the different number of rays, into four different subfamilies: A, with three radial spines (Triplagida and Triplectida); B, with four radial spines (Tetraplagida and Tetraplectida); C, with six radial spines (Hexaplagida and Hexaplectida); and D, with numerous (seven to nine or more) radial spines (Polyplagida and Polyplectida). The last three subfamilies have arisen probably from the first triradial subfamily, by a secondary increase in the number of rays.

The important signification of the triradial structure, recurring in the most different groups of Nassellaria, has been already pointed out sufficiently by myself and by R. Hertwig. But the triradial Plectoidea offer also another interesting relation of this characteristic structure, some simple forms of this order appearing nearly identical with the isolated triradial spicula of certain Beloidea (Thalassosphærida and Sphærozoida). Even some more complex quadriradial and sexradial forms of the latter reappear in exactly the same shape also in the former. This identity may be perhaps an important indication of true affinity (compare below).

The simplest and probably the most original kind of triradial structure is exhibited by the genera Triplagia and Triplecta (Pl. 91, figs. 2, 7). Here three equal radial spines lie in one horizontal plane and are united in a common central point at equal angles, so that three lines connecting their distal ends form a regular equilateral triangle. Simple triradial spicula of the same regular form are also found in many {901}Beloidea (Lampoxanthium, Sphærozoum, &c., Pls. 2 and 4). The central capsule of these simplest Plectoidea (with vertical main axis) rests perpendicularly on the horizontal triangle, formed by the triradial skeleton; the porochora of the former (or the "area porosa") rests upon the central point of the latter.

Another kind of triradial structure characterises the genera Plagiacantha and Plectophora. The three radial spines united in the central point lie here not in one plane, but diverge in different planes, so that they correspond to the three lateral edges of a three-sided pyramid. Commonly the three spines are of equal size, and also the angles between them equal, so that the pyramid is regular, sometimes very flat, at other times more elevated. Spicula of exactly the same form are also found in some Beloidea. Probably the three divergent spines are homologous to the three basal feet of numerous Spyroidea and Cyrtoidea. The central capsule, according to Hertwig, is placed in the apical part of the pyramid, the axes of both being identical, and the porochora resting in the apex itself. This fact seems to contradict the above-mentioned affinity; but since in Triplecta and Triplagia the three spines lie horizontally, they may have changed this original position in different direction, in Plagiacantha and Plectophora becoming divergent upwards, whereas in Plagoniscus and Plectaniscus (as in the Spyroidea and Cyrtoidea) directed downwards.

The triradial structure, common to the Triplagida and Triplectida, is replaced by the quadriradial structure in the Tetraplagida and Tetraplectida. Probably the latter have been derived from the former by development of a fourth spine, and then this latter would correspond to the "apical horn" of the other Nassellaria. But possibly also both structures have originated independently from one another. We may distinguish not less than four different kinds of the quadriradial structure. In the first case all four spines are equal, and diverge from a common central point at equal angles in different directions, corresponding to the four axes of a regular tetrahedron (Tetraplagia and Tetraplecta, Pl. 91, figs. 3, 8).

In the second case all four spines are also equal, but they are not united in a common central point, but opposite in pairs on the two poles of a common central rod (Plagonidium). Therefore the skeleton possesses here the same form as in the "geminate-biradiate" spicula of many Beloidea (e.g., Thalassoxanthium bifurcum and Sphærozoum furcatum). The development of the short horizontal middle rod, connecting the two divergent pairs of spines, is here probably effected by the porochora of the central capsule resting upon it.

Whilst in these two cases of quadriradial structure all four spines are equal, in two other cases they become differentiated in a very remarkable manner. One spine is vertically directed upwards, in shape and size different from the three others, which are directed downwards; the former corresponding probably to the "apical horn," the latter to the three "basal feet," which are found in the great majority of the Spyroidea {902}and Cyrtoidea. Therefore we encounter here for the first time that characteristic "cortinar structure" which is complete in Cortina and Cortiniscus (Pl. 92, figs. 11-13, 21), and which may be regarded as the strongest argument for a close relationship, or even for a common monophyletic origin of all Nassellaria.

The four spines, which we regard therefore as "cortinar spines," exhibit a twofold kind of central junction. In the simpler case they are united in a common central point, on which rests the porochora of the central capsule (Plagoniscus and Plectaniscus, Pl. 91, figs. 4, 9). These forms are nearer to Cortina, and may be derived immediately from Tetraplagia and Tetraplecta by differentiation of the four equal spines. In the other case the four cortinar spines are separated in pairs, diverging from the two poles of a short horizontal common "central rod" (Plagiocarpa and Periplecta, Pl. 91, figs. 5, 10). These forms may be compared with the spicula of some Beloidea and derived from Plagonidium; but their basal central rod may be compared again with the basal part of the sagittal ring of Cortina, and this comparison becomes very important in those forms like Plagiocarpa procortina (Pl. 91, fig. 5). Here the four spines approach very nearly to those of Cortina; the two ventral spines (or pectoral feet) on the anterior pole of of the middle rod are equal, but very different from the two dorsal spines, arising from the posterior pole; the lower odd spine of the latter corresponds to the "caudal foot," the upper spine to the "apical horn" of Cortina and of the Cyrtellaria. The vertical plane, determined by these two dorsal spines, is the sagittal plane, and two opposite curved branches which lie in this plane (an upper arising from the basal part of the apical spine and a lower arising from the anterior pole of the middle rod) may be regarded as ventral parts of an incomplete sagittal ring. This interesting form and some other similar Tetraplagida may be regarded either as beginning Stephoidea (Cortina, with incomplete sagittal ring) or as retrograde Stephoidea (Cortina, with partly reduced sagittal ring). In every case they seem to indicate the near relationship between the Stephoidea and Plectoidea.

Another argument for this close relationship may be found in the position of the central capsule in the interesting genus Plagiocarpa (Pl. 91, fig. 5). Its basal part (with the porochora) rests upon the common central rod, its ventral face upon the ventral prolongation of the latter, its dorsal face upon the apical horn; its axis lies in the sagittal plane. The three basal spines (the odd caudal and the paired pectoral feet) diverge from its basal pole downwards in the same manner as in the Cortina, the Zygospyrida and the Monocyrtida.

Less important than those quadriradial Tetraplagida and Tetraplectida, are the sexradial Plectoidea, the Hexaplagida and Hexaplectida. These may be derived immediately from the triradial Plectoidea by prolongation of the three primary original spines (of Plagiacantha) over the common central point. Here also two {903}different kinds of central junction are found. In the simpler case all six radial spines arise from a common central point (Hexaplagia and Hexaplecta). In the other case the six radial spines arise from the two poles of a short horizontal common central rod, opposed in two groups, each of three spines (Plagonium and Plectanium, Pl. 91, figs. 6, 11). In this latter case the single corresponding spines of the two opposite groups are usually parallel, and exhibit therefore exactly the same characteristic "germinate-triradiate" form which is found in many Beloidea (e.g., in the common Sphærozoum punctatum and the similar Lampoxanthium punctatum).

The fourth and last group of this suborder contains the multiradiate Plectoidea, the Polyplagida and Polyplectida. Here the number of radial spines, diverging from the common centre, exceeds six, and is commonly seven to nine, at other times ten to twelve or more (Polyplagia and Polyplecta, Pl. 91, fig. 12). When these two genera are better known from further accurate observations, they may probably be divided into several different genera (as already proposed in my Prodromus, 1881), since not only the number, but also the central junction and the arrangement of the numerous radial spines in the few observed species seems to be very different. In some seven-radiate species (e.g., Polyplecta heptacantha) four larger spines seem to be true "cortinar spines," the three smaller secondary productions of the former. In the nine-radiate species the nine spines seem to be sometimes basal branches of three primary spines, at other times six secondary intercalated between the three primary (like Enneaphormis, Pl. 57, fig. 9). In those multiradial Plectoidea, in which the number of spines amounts to ten or twelve or more, the laws of disposition are not yet recognised.

Comparing these different productions of the skeleton in the numerous Plectoidea, we find expressed two remarkable and very different affinities. On the one hand many Plectoidea exhibit exactly the same peculiar forms, which are only found besides in the Beloidea (as many species of Triplagia, Plagiacantha, Tetraplagia, Plagonidium, Hexaplagia, and Plagonium). On the other hand many Plectoidea bear the same characteristic composition of the skeleton (or the "cortinar structure") which is found in the Cortinida among the Stephoidea, and in numerous Spyroidea and Cyrtoidea, which all agree in the possession of three divergent basal feet and a vertical apical horn. A most important argument for the close affinity of all these "cortinar Nassellaria" seems to be given by the fact that the sagittal ring, which in Cortina is combined with the quadriradial structure, exhibits in the Cyrtellaria the most different stages of development; in one group it is complete, in the second incomplete, and in the third it has completely disappeared.

The form of the radial spines composing the skeleton is usually three-sided prismatic, gradually tapering from the thicker central base towards the distal apex; sometimes they are slender pyramidal. More rarely the spines are cylindrical or slender conical. In the majority of species the spines are straight, in the minority more or {904}less curved. In very few species only are they quite simple, without branches. They are nearly always more or less branched, in many larger species very richly ramified. The modes of ramification are rather variable. In the majority of Plectoidea the spines are rather regularly verticillate, bearing an increasing number of verticils, each of which is composed of three divergent branches. These arise from the three edges of the spine, and all the branches of one edge are usually parallel, either perpendicular to the spine, or directed at an acute angle towards its apex. When the verticils are numerous (five to ten or more), their size commonly tapers gradually towards the apex. Pinnate spines occur more rarely than verticillate ones; in this case the two paired lateral edges only of the prismatic spine bear opposite or alternate branches, whilst the odd middle edge bears no ramules. In some species the spines are singly or doubly forked. In many species (mainly those with cylindrical spines) the ramification of the spines is more or less irregular.

Whilst in all Plagonida the branches of the spine remain perfectly free, in all Plectanida, again, the meeting ends of the branches become united and grow together, and by this concrescence a loose network arises, like wickerwork, which partly encloses the central capsule and the central parts of the spines, on which it rests. The meshes of this loose wickerwork are large, either quite irregular, of very different size and form, or more or less regular, with a certain form and arrangement of the meshes, effected by the peculiar kind of ramification. Commonly the siliceous threads of the arachnoidal wickerwork are very thin, often extremely delicate, representing "pseudopodia metamorphosed into silex." Sometimes the wickerwork is spongy. Its surface is constantly rough and bristly, with free ends of the spine-branches, never covered with a regular lattice-plate, as in the Cyrtellaria (Spyroidea, Botryodea, and Cyrtoidea).

The entire form of the central wickerwork is in the minority of Plectanida quite irregular and indefinite; in the majority, however, a certain more or less regular entire form is recognisable, effected by a certain, more or less regular origin and mode of the connection of the meeting branches. So in some species of Triplecta (Pl. 91, fig. 7) the network represents a triangular plate, of Plectophora and Plectaniscus a three-sided pyramid, of Tetraplecta (Pl. 91, fig. 3) a tetrahedron, and in many other species a polyhedron of more or less regular form. Some species of Plectanida become very similar to certain species of Stephoidea, Spyroidea, and Cyrtoidea; so Plectaniscus and Periplecta approach to Cortina and Cortiniscus, Pteroscenium and Clathrocorys, &c. (compare Pls. 92, 93, 53, 64, &c.). They may represent a true phylogenetic connection between both groups. But in these cases also the distinction is determined by the fact that the true Plectoidea never possess a complete sagittal ring (like the Stephoidea) nor a regular lattice-shell (like the Spyroidea, Botryodea, and Cyrtoidea).

The Central Capsule of the Plectoidea constantly exhibits the peculiar characters of the Monopylea or Nassellaria. It is commonly ovate, more rarely ellipsoidal or even spherical, sometimes conical or lentelliptical. The lower or basal pole of its vertical main axis constantly exhibits the characteristic "porochora" (or the area porosa) of the Monopylea, and upon this rests the peculiar "podoconus" (or the pseudopodial-cone) of this legion. On this porochora the central capsule is in immediate connection with the central point of the skeleton, or the horizontal common central rod, from which the radial spines arise. The endoplasm, or the protoplasm of the central capsule (besides the podoconus), contains commonly one large alveole or several small vacuoles, and often pigment-granules. The nucleus is large, spherical or ovate, and exhibits the same character as in all the other Monopylea; it encloses usually a single nucleolus.

The position of the central capsule and its topographical relation to the skeleton offers in the different Plectoidea some important and as yet unsolved problems, which can be answered only by fresh and accurate observations on living specimens. In Triplagia and Triplecta, where the triangular skeleton lies in a horizontal plane, the vertical main axis of the central capsule is perpendicular to the central point of that supporting triangle. In Plagiacantha and Plectophora, where the three radial spines correspond to the edges of a flat pyramid, the capsule is enclosed in the pyramidal space of the latter, its basal pole touching the apex; therefore in the normal position of the body the three divergent rays are directed upwards. In Tetraplagia and Tetraplecta probably the same position is retained, and therefore the fourth free spine, here developed, is probably directed vertically downwards. In Plagoniscus and Plectaniscus, however, and moreover, in the closely allied Plagiocarpa and the corresponding Periplecta (Pl. 91, figs. 5, 10) the position of the central capsule, relative to the skeleton, seems to be inverse, and to agree with that of the Stephoidea (Cortina, Cortiniscus, &c.) and the Cyrtoidea (Pteroscenium, Clathrocorys, &c.); the three divergent spines are here directed downwards (as basal feet), whilst the opposite fourth spine is vertically directed upwards (as an apical horn); the capsule rests here upon the tripod, which lies below it, and is inclined with its dorsal face to the apical spine. In the majority of the other Plectoidea the position of the central capsule and its relation to the skeleton are not yet sufficiently observed, and require further accurate researches. Its position seems to be very different in the several genera. The capsule is never perforated by parts of the skeleton; this latter is constantly extra-capsular.

The physiological value of the skeleton, with regard to the central capsule, is different in the Plagonida and Plectanida; in the former it supports, in the latter it encloses the capsule like a shell. In the Nassellida, where no skeleton is developed, the central capsule is quite free and naked, enveloped only by the calymma.

The calymma or the extracapsular jelly-veil in all Plectoidea is voluminous, and encloses not only the central capsule completely, but also the skeleton wholly or partially. Its form is of the greatest value for the development and configuration of the skeleton. Sometimes the calymma is alveolate and foamy, as in Nassella and the common Thalassicolla. In several other Plectoidea the calymma seems to include numerous small vacuoles, sometimes also pigment-granules. Xanthellæ are commonly scattered in it in great numbers. The pseudopodia, arising in a large bunch from the porochora of the capsule, and running along the branches of the radial spines, seem to be always numerous, richly branched, and with a strong tendency to form anastomoses. The peculiar form of their network is often exactly preserved in the conformation of the skeleton, produced by them. The peculiarities of this network require further accurate observations, as does the whole organisation of the Plectoidea.

Synopsis of the Families of Plectoidea.

Family XLVI. Plagonida, Haeckel.

Plagonida, Haeckel, 1881, Prodromus, p. 423.

Plagiacanthida (sensu strictiori), Richard Hertwig, 1879, Organismus d. Radiol., p. 72.

Definition.—Plectoidea with a spiny skeleton, composed of radial spines, which arise from a common central point or central rod, and support the free central capsule.

The family Plagonida comprises those Nassellaria in which the skeleton is only composed of united radial spines, arising from a common centre, without any connection of meeting branches of the spines; the rudimentary skeleton exhibits therefore neither a loose wickerwork (as in the closely allied Plectanida), nor a ring (as in the Stephoidea), nor a complete lattice-shell (as in the Cyrtellaria, the Spyroidea, Botryodea, and Cyrtoidea). The central capsule, which possesses all the characters of the Monopylea, is therefore free, not enclosed, and only on one side supported or partly protected by the radial spines or their branches.

Two species only of Plagonida have been hitherto known. The first form described is the Plagiacantha arachnoides, discovered thirty years ago (1855) by Claparède on the western shore of Norway. Another species of the same genus, from the Mediterranean, was very accurately described by Richard Hertwig in 1879 in his Organismus der {907}Radiolarien (Plagiacantha abietina). Upon these two species the latter founded his family Plagiacanthida, a term which was afterwards employed by Bütschli and others, for the whole group of Plectoidea. Many new forms are contained in the collection of the Challenger, so that we may describe here nine genera and thirty-four species.

The family Plagonida may be divided into four different subfamilies, according to the numbers of the radial spines which compose the skeleton: Triplagida with three, Tetraplagida with four, Hexaplagida with six, and Polyplagida with numerous (seven to nine or more) radial spines. These are united commonly in one common central point, upon which rests the basal pole of the central capsule, with the porochora. More rarely (in the genera Plagonidium, Plagiocarpa, and Plagonium) the spines arise in two opposite groups (each with two or three spines) from the two poles of a common central rod; in this case the basal pole of the central capsule with the porochora rests upon the horizontal common rod, which corresponds probably to the basal part of the sagittal ring of the Stephoidea and Cyrtellaria.

The different forms which the skeleton of the Plagonida assumes in the different genera of this family, and the important relations which these exhibit on the one hand to the spicula of the Beloidea, and on the other hand to the shell of some Stephoidea (Cortina, Cortiniscus, &c.) and Cyrtoidea (Pteroscenium, Clathrocorys, &c.), have been already pointed out in the preceding description of the suborder Plectoidea. There it is also demonstrated, that all these different forms may be derived from the simplest triradial forms, Triplagia and Plagiacantha (compare above, pp. 900-904).

Whilst the genera of the Plagonida are characterised by the number of the radial spines and the peculiar mode of junction in a common central point or at the two poles of a common central rod, the different species of this family may be defined by the peculiar form of the spines and their branches. These morphological characters have also been already described above. We repeat here only that the radial spines in the majority of species are three-sided prismatic and verticillate, each verticil commonly with three branches. The distal ends of these branches remain constantly free, and are never united, as is always the case in the following family.

The Central Capsule of the Plagonida exhibits the general characters of all Monopylea (compare above, p. 890). It is commonly ovate or ellipsoidal, with vertical main axis; on the lower pole of the latter is the porochora (or the "area porosa," from which all pseudopodia radiate). This is in immediate connection with the central point or central rod of the skeleton, in which its radial spines are united. The topographical relation of the supporting skeleton to the central capsule seems to exhibit in the different genera of the Plagonida remarkable differences, as already demonstrated above (p. 905).

Synopsis of the Genera of Plagonida.

Subfamily 1. Triplagida, Haeckel, 1881, Prodromus, p. 423.

Genus 384. Triplagia,^[3] Haeckel, 1881, Prodromus, p. 423.

Definition.—Plagonida with three radial spines, arising from one common central point and lying in one horizontal plane.

The genus Triplagia and the following closely allied Plagiacantha may be regarded as the simplest and most primitive forms of the Plectoidea, perhaps as the common ancestral stock of this suborder. The skeleton is composed of three simple or branched radial spines, arising from one common central point. These three spines in Triplagia lie in one and the same plane, whilst in Plagiacantha they lie in different planes. Therefore the former exhibits the simplest type of the triradial structure, common to the majority of Nassellaria.

Spines straight, of equal size and similar form, equidistant, three-sided prismatic, each with two pairs of opposite lateral branches, which are correspondingly parallel to the two other spines; the proximal branches twice as long as the distal branches.

Spines straight, of equal size and similar form, equidistant, three-sided prismatic, regularly pinnate, with six pairs of opposite pinnulæ, tapering gradually towards the distal ends; the basal pinnulæ are again branched, with straight ramules.

Spines curved, cylindrical, irregularly branched, with three primary and nine to twelve secondary branches, which are also slightly curved. The angles between the bases of the three spines are equal, but the size and form of the branches different.

Dimensions.—Length of the three spines 0.15 to 0.25, of the basal branches 0.05 to 0.08.

Genus 385. Plagiacantha,^[4] Claparède, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, November 13.

Definition.—Plagonida with three radial spines, arising from one common central point and corresponding to the edges of a three-sided pyramid.

The genus Plagiacantha agrees with the preceding Triplagia in the simple structure of the triradial skeleton, composed of three diverging radial spines, which are united in a common centre at the oral pole of the central capsule. But whilst the three radial rods of Triplagia lie in one horizontal plane, here they lie in different planes and correspond to the three edges of a flat pyramid. Plagiacantha arachnoides, described in 1856 by Claparède, was the earliest known form of all Plectoidea.

Plagiacantha arachnoides, Claparède, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, November 13.

Plagiacantha arachnoides, Claparède, 1858, Études sur les Infusoires et les Rhizopodes, p. 462 (pl. xxii. fig. 8).

Acanthometra arachnoides, Claparède, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 675.

Spines straight, cylindrical, divided into three divergent straight branches of equal size; each branch two to three times as long as the simple thicker basal part.

Spines straight, cylindrical, divided into two divergent straight branches of equal size, of about the same length as the simple basal part. The spines and their branches are smooth.

Spines straight, three-sided prismatic, in the middle with one verticil composed of three divergent straight branches of equal size, of about the same length as the simple basal part. The edges of the spines and their branches are thorny.

Plagiacantha abietina, Richard Hertwig, 1879, Organismus d. Radiol., p. 72, Taf. vii. figs. 6-6b.

Spines straight, three-sided prismatic, with three verticils of three divergent straight lateral branches, decreasing in size towards the distal end; the branches of the first verticil about twice as long as those of the second, and four times as long as those of the third verticil. All nine branches of each spine simple, straight, three-sided pyramidal.

Dimensions.—Length of the spines 0.2 to 0.3, of the basal branches 0.06 to 0.08.

Spines curved, three-sided prismatic, with six to nine verticils of three divergent branches, decreasing in size towards the distal end; the branches of the first verticil about twice as long as those of the fourth verticil. All branches simple, slightly curved, bristle-shaped.

Spines straight, three-sided prismatic, with prominent wing-like edges and ten to twelve verticils of three divergent branches, decreasing in size towards the distal end; the branches of the three or four basal verticils are again ramified and much larger than the simple branches of the distal verticils.

Subfamily 2. Tetraplagida, Haeckel, 1881, Prodromus, p. 424.

Genus 386. Tetraplagia,^[5] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plagonida with four equal radial spines, arising from one common central point, and corresponding to the four axes of a tetrahedron.

The genus Tetraplagia is one of the most important Plectoidea, and possibly the common ancestral form of many Nassellaria (compare above, p. 901). The skeleton is composed of four radial rods, diverging from one common centre in different directions, and corresponding to the four axes, which extend from the central point of a tetrahedron to the central points of its four faces. The whole skeleton of Tetraplagia exhibits therefore the same form, which is observed in the single quadriradiate spicula of some Beloidea (in some species of Lampoxanthium, Sphærozoum, &c.).

Spines straight, cylindrical, perfectly equal, corresponding in regular disposition exactly to the four geometrical axes of a regular tetrahedron; in the middle arise from each spine two opposite equal lateral branches of half the length of the spine.

Spines straight or slightly curved, three-sided prismatic, with irregular short branches arising from the three edges; the branches are thorny, tapering towards the apex.

Plagiacantha abietina, var. quadrispina, Richard Hertwig, 1879, Organismus d. Radiol., p. 73.

Spines straight, three-sided prismatic, verticillate, with six to eight verticils of three simple straight branches; the branches of each edge are parallel, tapering towards the distal end. R. Hertwig regards this species only as a four-spined variety of his three-spined Plagiacantha abietina; but a specimen, observed by me in Corfu, exhibited all the characters of Tetraplagia.

Genus 387. Plagoniscus,^[6] n. gen.

Definition.—Plagonida with four unequal radial spines, arising from one common central point; one vertical or apical spine opposed to three divergent or basal spines.

The genus Plagoniscus agrees with the preceding Tetraplagia (its probable ancestral form) in the possession of four radial spines, diverging from one common central point. But whilst in this latter all four spines are equal, corresponding exactly to the four axes of a tetrahedron, here in Plagiocarpa an important difference exists between one vertical or apical spine and three other divergent basal spines; these latter corresponding probably to the three "feet," the former to the single "apical horn" of the majority of Nassellaria. Perhaps we find here one of the oldest and simplest types of their "triradial or cortinar structure" (compare above, p. 902).

Spines three-sided prismatic, thorny. Apical spine nearly straight, verticillate, with four to five verticils of three thorny branches, tapering towards the apex. Three basal spines somewhat shorter, curved, with three thorny edges.

Spines three-sided prismatic, thorny, with dentate edges, and three to six verticils of three short branches. Apical spine straight, with six verticils, nearly twice as long as the three curved basal spines, each of which bears three verticils; the basal verticils larger and ramified. Resembles somewhat Euscenium eucolpium, Pl. 53, fig. 12, but has no latticed shell.

Spines three-sided prismatic, straight, verticillate. Apical spine with twelve verticils, one and a half times as long as the three basal spines, each of which bears eight verticils of three branches. The branches are also prismatic, straight, on each edge parallel, tapering towards the apex, in the three basal spines forked, in the apical spine more branched. Similar to the cortinar skeleton of Clathrocorys (Pl. 64, figs. 8-10).

Spines cylindrical, curved, irregularly branched. Apical spine half as long as, and less branched than the three basal spines, which are sigmoidal, nearly horizontally expanded in the proximal half, descending in the distal half.

Genus 388. Plagonidium,^[7] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plagonida with four equal radial spines, arising in pairs from the two poles of a common central rod.

The genus Plagonidium, and the following Plagiocarpa possess four radial spines, like the two preceding genera. But whilst the four rods in these latter arise from a common centre, here they arise in two pairs from the two poles of a common middle rod; they have therefore exactly the same form which we find in the single spicula of some Beloidea (e.g., Thalassoxanthium furcatum, Sphærozoum furcatum, &c.). Probably the middle rod is horizontal and serves as supporting base for the central capsule, whilst two opposite spines are directed upwards, two other downwards.

Spines straight, three-sided prismatic, four to six times as long as the common central rod, pinnate, with four to five pairs of opposite pinnulæ, the distal of which are simple, the proximal again branched.

Spines cylindrical, curved, eight to ten times as long as the common central rod, in the distal half forked; the fork-branches curved, somewhat longer than the basal part.

Genus 389. Plagiocarpa,^[8] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plagonida with four unequal radial spines, arising in pairs from the two poles of a common central rod; one ascending apical spine opposed to three descending basal spines.

The genus Plagiocarpa agrees with the preceding Plagonidium in the possession of a common horizontal middle rod, the two poles of which bear two pairs of divergent spines; but whilst in the preceding all four spines are equal, here they are differentiated in the same manner as in Plagoniscus, which differs only in the absence of the middle rod. The two observed and closely allied species of this genus are of peculiar interest, since they belong possibly to the common ancestral forms of the Nassellaria; the basal middle rod corresponds perhaps to the basal part of a sagittal ring, the apical spine to its dorsal part, the three other spines to the basal feet (compare above, p. 902).

Spines cylindrical, curved, thorny, three to four times as long as the common middle rod. Apical spine and the meeting caudal spine (or the posterior basal spine) somewhat longer and with more numerous thorns than the two paired pectoral (or anterior) spines. From the common base of the latter arises an anterior prolongation of the horizontal middle rod, which in the sagittal plane is curved upwards and corresponds to the sternal foot of many Cyrtellaria. An ascending branch of this spine is opposed to a descending branch of the apical spine, both together forming an incomplete sagittal ring.

Spines of form and arrangement similar to those of the preceding species, but longer and more branched, six to eight times as long as the shorter common middle rod. The two characteristic {915}opposed branches (the ascending branch of the basal rod and the descending branch of the apical spine), which in the preceding species nearly compose a sagittal ring, are here absent.

Subfamily 3. Hexaplagida, Haeckel.

Genus 390. Hexaplagia,^[9] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plagonida with six radial spines, arising from one common central point.

The genus Hexaplagia differs from the preceding genera of Plagonida in the possession of six radial spines, diverging from one common central point. Commonly, these six spines seem to lie opposite in pairs in three different meridian planes, and in this case Hexaplagia may be regarded as a Plagiacantha, the three radial spines of which are prolonged over the basal pole of the central capsule. But in other species the six spines seem to lie in different planes. Further observations are required.

Spines opposite in pairs in three diameters, crossed in the common centre, straight, three-sided prismatic, with dentate edges. The three pairs are equal, but the upper spine of each pair only half as long as the lower spine.

Spines opposite in pairs in three diameters, crossed in the common centre, slightly curved, three-sided prismatic, with verticillate branches; the three pairs are equal, but the lower spine of each pair bears three to four verticils, each of three branches, and is two to three times as long as the upper spine, which bears two verticils only.

Spines in opposite pairs in three diameters, crossed in the common centre, straight, cylindrical, pinnate, with three to four pairs of opposite lateral branches or regular pinnulæ. All six spines are equidistant, of equal size and similar form, and lie with their branches nearly in one horizontal plane. Therefore they are similar to the six radial rods in the collar septum of many Spyroidea and Cyrtoidea (e.g., Calpophæna, Pl. 53, fig. 18).

Spines unequal, at unequal intervals, not opposite in pairs, cylindrical, irregularly branched and curved. In this species a definite arrangement of the six different spines could not be detected.

Genus 391. Plagonium,^[10] Haeckel, 1881, Prodromus, p. 423.

Definition.—Plagonida with six radial spines, arising in two opposite divergent groups from the two poles of a common central rod.

The genus Plagonium differs from the preceding closely allied Hexaplagia in the remarkable peculiarity, that the six radial spines do not arise from one common central point, but from the two poles of a common horizontal middle rod; three divergent spines on each pole. The skeleton of Plagonium exhibits therefore the same remarkable form which is found in the isolated spicula of numerous Beloidea (e.g., Lampoxanthium punctatum, Sphærozoum punctatum), and bears the same relation to Hexaplagia that Plagonidium does to Tetraplagia.

Spines straight and stout, three-sided prismatic, about twice as long as the common middle rod, irregularly branched or nearly verticillate, with short thorny branches. Similar to the single spicula of some species of Sphærozoum and Lampoxanthium.

Spines irregularly curved, slender, cylindrical, six to eight times as long as the common middle rod, in the proximal half smooth, in the distal half covered with short thorns. (Similar to an isolated spiculum of Lampoxanthium punctatum or of Sphærozoum variabile, Pl. 4, fig. 5.)

Spines irregularly curved and branched, slender, cylindrical, thorny, twelve to sixteen times as long as the middle rod; the branches are large, arborescent, their ramules again ramified and very thorny.

Spines straight, slender, cylindrical, four to six times as long as the middle rod, in the basal half smooth, in the distal half arborescent, with three to four irregular verticils of ramified branches. (Similar to a single spiculum of Sphærozoum verticillatum, Pl. 4, fig. 7.)

Spines straight and stout, three-sided prismatic, smooth, ten to twelve times as long as the middle rod; each on the distal end cleft into three divergent straight branches, which are again trichotomous.

Subfamily 4. Polyplagida, Haeckel, 1881, Prodromus, p. 424.

Genus 392. Polyplagia,^[11] n. gen.

Definition.—Plagonida with numerous (seven to nine or more) radial spines, arising from a common centre and lying in different planes.

The genus Polyplagia alone represents the small subfamily of Polyplagida, distinguished from the other Plagonida by the multiplication of the radial spines, the number of which amounts to seven to nine or more. This increased number is commonly the result of an intercalation of new spines between the three or four primary spines; it is sometimes also effected by stronger development of branches of the latter, which become independent. The following five species of this genus are very different, require further investigation, and perhaps represent different genera:—

Seven radial spines, straight, three-sided prismatic, verticillate, of different sizes; four larger spines correspond to the four axes of a tetrahedron (running from the centre to the four corners), each with five to six verticils of three simple slender branches; one of these four main spines seems to be the apical, the three others the basal spines of Plagiocarpa; in the three meridian planes between the latter and the former lie the three smaller spines, diverging upwards, each with two to three verticils. (Similar to Polyplecta heptacantha, Pl. 91, fig. 12, but without connection between the branches.)

Eight radial spines, straight, three-sided prismatic, of equal size, arising in two opposite groups from the two poles of a short common middle rod (as in Sphærozoum arborescens, Pl. 4, fig. 8, and in other Beloidea). The four spines of each group are divergent, six to eight times as long as the middle rod, each spine armed with three to four verticils of thorny branches.

Nine radial spines of equal size, straight, cylindrical, lying nearly in a horizontal plane, or forming a very flat pyramid. Near the common central point every three spines arise from a short common rod, so that the centre of the skeleton is triradial. Each spine bears towards the apex two divergent straight lateral branches. This species may have been derived from Plagiacantha arachnoides by shortening and reduction of the basal parts of the three original branched primary spines.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray, surface.

Twelve radial spines of equal size, arising from a common central point, and diverging in different directions. The twelve spines are very large, opposite in six pairs, cylindrical, longitudinally {919}striped (the expression of concentric lamellæ), and with spinulate surface, covered with innumerable small thorns. The basal quarter of each spine is straight and simple, the second quarter twice forked, and these four fork-branches are again in the outer half of the spine richly forked or ramified, with diverging, slightly curved thin branches; each of the twelve spines with about sixty to eighty terminal branches, the ends of which seem to fall into a spherical face. The position of this remarkable species in this family is doubtful.

Dimensions.—Length of the spines 0.12 to 0.16, of the simple basal part 0.04.

Numerous (sixteen to twenty or more) radial spines of about equal size, arising from a common central point and diverging in different directions, richly and more or less irregularly branched. The ends of the numerous small branches seem to fall into a spherical face. The large spines of this species have the same form and structure as in the preceding, nearly allied species, but are more numerous and more irregularly branched and disposed.

Dimensions.—Length of the spines 0.2 to 0.25, of the simple basal part 0.05.

Family XLVII. Plectanida, Haeckel.

Plectanida, Haeckel, 1881, Prodromus, p. 424.

Definition.—Plectoidea with a wattled skeleton, composed of the meeting and united branches of radial spines, which arise from a common central point or central rod, and protect the partly enclosed central capsule.

The family Plectanida comprises those Nassellaria in which the skeleton is composed of radial spines, arising from a common centre, and of a loose wickerwork, produced by concrescence of the meeting branches of those spines. This rudimentary wattled skeleton is either quite irregular or only slightly regular, but it never assumes the form of a complete lattice-shell, as in the Cyrtellaria (the Spyroidea, Botryodea, and Cyrtoidea), nor does it exhibit a ring (as in the Stephoidea). The central capsule is partly or wholly protected, and often entirely enclosed by the wattled skeleton.

Three species only of Plectanida have been hitherto known. The first described form is Plectophora arachnoides, which its discoverer Claparède observed in a living state in 1855 on the western coast of Norway, and considered as a mere variety of his Plagiacantha arachnoides. Two other species were afterwards observed in the Mediterranean, Polyplecta dumetum, 1856, by Johannes Müller (united by him with Acanthodesmia) and Polyplecta polybrocha by myself in 1864. Many new forms are found in the {920}collection of the Challenger, so that we may here distinguish eight genera and twenty-seven species.

The family Plectanida may be divided into four different subfamilies, according to the number of the radial spines which compose the skeleton. Those four subfamilies, as also the genera contained in them, correspond exactly to the four subfamilies of Plagonida, from which they have originated: Triplectida with three, Tetraplectida with four, Hexaplectida with six, and Polyplectida with numerous (seven to nine or more) radial spines. These spines are usually united (as in the corresponding ancestral Plagonida) in one common central point, upon which rests the basal pole of the central capsule, with the porochora. More rarely (in the genera Periplecta and Plectanium) the spines arise in two opposite groups (each of two or three spines) from the two poles of a common horizontal central rod, which supports the overlying porochora of the central capsule.

The different genera of Plectanida, which are enumerated in the following synopsis, correspond so exactly to the different genera of Plagonida described above, that probably each of the former has arisen from a corresponding genus of the latter. The only difference between the two is, that in all Plagonida the branches and ramules of the radial spines end freely, without growing together, whilst in all Plectanida the meeting ends of the neighbouring spines grow together and so produce a loose and irregular wickerwork. Therefore the latter constantly possess meshes, which are missing in the former. As soon as any form of Plagonida begins to produce meshes by concrescence of meeting branches of the spines, it passes over into a corresponding form of Plectanida. The loose wickerwork or wattlework so produced is sometimes very irregular, at other times more or less regular; but it never assumes the regular form of a complete lattice-shell, as in the Cyrtellaria (Spyroidea, Botryodea, and Cyrtoidea). The general differences which this wickerwork exhibits in the different genera of Plectanida have been already described above (compare pp. 900-904).

The Central Capsule of the Plectanida agrees perfectly with that of the ancestral Plagonida, as well in general form and structure as in the peculiar topographical relation to the radial spines (compare above, p. 905). A slight difference between the two families is effected by the higher development of the skeleton in the Plectanida. Since the branches of the radial spines in this family become united and form a loose wickerwork, the central capsule becomes more or less enclosed by the latter, and more perfectly protected, than in the Plagonida, where the branches remain free. In this respect the Plectanida approach more nearly to the Cyrtoidea with which they are connected by such transitional forms as Plectaniscus and Periplecta on the one hand, Cladoscenium and Pteroscenium on the other.

Synopsis of the Genera of Plectanida.

Subfamily 1. Triplectida, Haeckel, 1881, Prodromus, p. 424.

Genus 393. Triplecta,^[12] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plectanida with three radial spines, arising from one common central point and lying in one horizontal plane.

The genus Triplecta is the simplest and most primitive of the Plectanida, and may therefore be regarded as the prototype of this family. The skeleton represents a triangular lattice-plate with three radial beams. On the central union of the latter rests the oral pole of the central capsule. Since the axis of the latter is vertical, the lattice-plate must be horizontal, serving for the expansion of the pseudopodia. Triplecta has arisen from Triplagia by union of the branches of its three radial spines. In the simplest case only three large meshes are formed, corresponding probably to the three cortinar meshes in the collar septum of many Cyrtellaria.

Spines straight, equal, smooth, cylindrical, each in the basal half with one pair of divergent straight lateral branches. The opposed branches of every two neighbouring spines are united by a {922}thin convex bow. In this way arises a very simple, equilateral triangular skeleton, with three equal large meshes.

Spines straight, equal, three-sided prismatic, pinnate, each with three to four pairs of opposite slender pinnulæ or lateral branches; the pinnulæ of each spine are correspondingly parallel to the main rods of the other two spines. All pinnulæ branched and connected by a few slender bows, marking the sides of a regular triangle.

Genus 394. Plectophora,^[13] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plectanida with three radial spines, arising from one common central point and corresponding to the edges of a three-sided pyramid.

The genus Plectophora has been derived from Plagiacantha by union of the meeting neighbouring branches of the three radial spines, and exhibits therefore to it the same relation that Triplecta bears to Triplagia. The loose framework so produced corresponds to the three sides of a flat pyramid and supports the central capsule.

Spines equal, straight, three-sided prismatic, thorny, connected by three convex bows, the meeting branches of lateral spines arising in one pair from the middle part of each spine. Therefore the skeleton exhibits three large ovate meshes only.

Plagiacantha arachnoides, var., Claparède, 1858, Études sur les Infusoires et les Rhizopodes, p. 462, Taf. xxii. fig. 9.

Spines straight, cylindrical, trifid, with one pair of lateral branches. The nine diverging, straight, and smooth branches are connected in the distal part by slender concave bows, so that the whole skeleton exhibits nine wide meshes, three larger pentagonal and six smaller triangular.

Spines slightly curved, three-sided prismatic, thorny, with two pairs of lateral branches. The six smaller distal branches end freely, whilst the six larger basal branches are connected by slender convex bows. There are therefore nine wide meshes, as in the preceding closely allied species.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream) (John Murray), surface.

Spines straight, three-sided prismatic, with three to four verticils of short lateral branches. The branches of the basal verticils are again ramified, and form by connecting bows a delicate loose framework, covering the three sides of a flat pyramid, the three edges of which are the three radial spines.

Subfamily 2. Tetraplectida, Haeckel, 1881, Prodromus, p. 424.

Genus 395. Tetraplecta,^[14] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plectanida with four equal radial spines, arising from one common central point and corresponding to the four axes of a tetrahedron.

The genus Tetraplecta has been derived from Tetraplagia by union of the neighbouring branches of the four radial spines, diverging from a common point in different directions. In some forms of this genus the four rods seem to correspond exactly to the four axes, which are directed from the centre of a tetrahedron towards its four corners; whilst in other forms the four rods and the angles between them are perhaps not perfectly equal.

Spines straight, equal, three-sided prismatic, pinnate, each with three or four pairs of opposite straight slender pinnulæ or lateral branches; the pinnulæ of each side are correspondingly parallel. {924}All pinnulæ connected by a few slender bridges, thus producing a delicate network with irregular rhomboidal meshes.

Spines in the basal half straight, in the distal half slightly curved and irregularly branched, with two to three pairs of unequal alternate lateral branches, the distal ends of which are connected by a few slender bows, marking the six edges of an irregular tetrahedron.

Spines three-sided prismatic, straight, or in the basal half slightly curved, verticillate; each spine with six to eight three-branched regular verticils, tapering gradually towards the distal end. All branches of each spine lie parallel in three equidistant meridian planes, and are connected by delicate parallel threads, perpendicular to the branches. Therefore the skeleton consists of four pine-shaped trees and twelve delicate triangular wings with rectangular meshes.

Dimensions.—Length of the spines 0.25 to 0.3, of the basal branches 0.1 to 0.15.

Genus 396. Plectaniscus,^[15] nov. gen.

Definition.—Plectanida with four unequal radial spines, arising from one common central point; one vertical or apical spine opposed to three divergent or basal spines.

The genus Plectaniscus has probably been derived from Plagoniscus by reticular union of the neighbouring branches of the four radial spines, and exhibits therefore to it the same relation that Tetraplecta bears to Tetraplagia. Whilst in these two latter genera the four spines are equal, in the two former genera there is an important difference between a vertical spine (or apical horn) and three divergent (commonly larger) spines, corresponding to the three basal feet of the triradiate Nassellaria. Perhaps, therefore, Plectaniscus is one of the remotest ancestors of the latter; but differs in the absence of a complete lattice-shell.

Spines straight, three-sided prismatic, with three to four verticils of short perpendicular branches; the branches of the distal verticils are simple and free, those of the proximal verticils again ramified and connected by an arachnoidal network of delicate threads. The vertical apical spine (or horn) is scarcely one-third or half as long as the three divergent basal spines (or feet), and the angle between it and the latter is smaller.

Dimensions.—Length of the apical spine 0.05 to 0.1, of the three basal spines 0.18 to 0.2.

Spines curved, cylindrical, with a variable number of irregular branches, which in the distal half of the spines are free, in the basal half again ramified and connected by a loose spongy framework. The apical spine is shorter and simpler, nearly straight, less ramified.

Dimensions.—Length of the apical spine 0.1, of the three basal spines 0.15 to 0.18.

Spines slightly curved, three-sided prismatic, with two to three verticils of short curved branches. The vertical apical spine is about twice as long as the three basal spines, and connected with them by an irregular loose framework. The three basal spines are connected together only by a simple ring, so that between them remain three large collar holes, like those of the similar and closely allied Archiscenium quadrispinum (Pl. 53, fig. 11).

Dimensions.—Length of the apical spine 0.32, of the three basal spines 0.18.

Spines curved, three-sided prismatic. The three basal spines pinnate, with four to five pairs of opposite curved pinnulæ; the distal pairs are simple and free, the basal pairs branched and connected by an irregular delicate framework, which together with the apical spine forms a spongy cap-shaped shell, similar to Cladoscenium. Apical spine about half as long, simple.

Spines straight, three-sided prismatic, with seven or eight verticils of ramified branches, which in the basal half are connected by an irregular loose framework. In the distal half each of the three divergent basal spines (or feet) is connected with the longer apical spine (or horn) by a {926}fenestrated triangular lattice wing. Therefore the skeleton becomes very similar to Clathrocorys (Pl. 64, figs. 8-10), but wants the regular central cephalis.

Genus 397. Periplecta,^[16] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plectanida with four unequal radial spines, arising in pairs from the two poles of a common central rod; one ascending apical spine opposed to three descending basal spines.

The genus Periplecta has probably been derived from Plagiocarpa (by concrescence of the meeting spine branches), and has the same important relation to a part of the triradial Stephoidea (Cortina, &c.) and Cyrtoidea (Pteroscenium, &c.). It differs from the latter only in the fact that the loose irregular framework connecting the bases of the four cortinar spines is not a regular lattice-shell.

Spines of very different size and shape, three-sided prismatic. The apical spine (or horn) is larger, nearly straight, and bears a verticil of three large divergent branches, which are again ramified. The three basal spines (or feet) are curved, pinnate, each with three to five pairs of opposite simple curved branches. A small common central rod separates the two united pectoral feet from the two other spines (the caudal foot and the apical horn). The three basal feet are connected by three convex bows composing a horizontal collar ring, and since the central rod is prolonged between the pectoral feet to the ring, a very remarkable collar septum is formed with four cortinar meshes. Above this septum an irregular spongy shell, including the central capsule, is formed by a delicate framework, interwoven between the apical horn and the three basal feet.

Dimensions.—Length of the apical spine 0.25 to 0.3, of the three basal spines 0.15 to 0.2.

Spines of very different size and shape, three-sided prismatic, verticillate. The apical spine (or horn) with ten to twelve verticils, is one and a half times as long as the three basal spines (or feet), which bear six to eight verticils only; each verticil with three branches which by communicating ramules form a loose irregular wickerwork. Similar to Pteroscenium pinnatum, Pl. 53, figs. 14-16, but without a regular lattice-shell. A short basal central rod separates two equal (pectoral) spines from two unequal spines, the larger of the latter is the apical, the shorter the caudal spine.

Dimensions.—Length of the apical spine 0.26, of the three basal spines 0.17.

Spines of nearly equal size and shape, cylindrical, irregularly branched. The apical spine is straight, more branched and nearly twice as long as the three basal spines. All four spines in the basal third connected by a loose spongy framework, approaching the form of some Monocyrtida.

Subfamily 3. Hexaplectica, Haeckel.

Genus 398. Hexaplecta,^[17] Haeckel, 1881, Prodromus, p. 425.

Definition.—Plectanida with six radial spines, arising from one common central point.

The genus Hexaplecta has probably been derived from Hexaplagia by concrescence of the meeting branches of the six spines, and therefore has to it the same relation that Plectophora bears to Plagiacantha. The two species here described represent perhaps two different genera, since in the first all six spines are equal, opposed in pairs, in the second different in pairs (three upper smaller and three lower larger).

Spines equal, opposite in three crossed pairs, straight, three-sided prismatic, thorny, in the distal half with three leaf-shaped, dentate edges, in the basal half with three verticils of slender branches, which are connected by parallel threads, and so form an arachnoidal network with rectangular or rhomboidal meshes.

Spines unequal, three larger spines (in the lower half of the body) being opposite to three smaller spines (in the upper half). The latter are nearly horizontally expanded, each bearing three straight divergent branches. The larger are stronger, twice as long and armed with three verticils, each of three branches. All six spines are slender, three-sided prismatic. Their branches are very thin, thread-shaped, and form by their union a loose network with irregular polygonal meshes.

Genus 399. Plectanium,^[18] Haeckel, 1881, Prodromus, p. 424.

Definition.—Plectanida with six radial spines, arising in two opposite divergent groups from the two poles of a common central rod.

The genus Plectanium has been derived from Plagonium by concrescence of the meeting branches, and bears therefore to it the same relation that the preceding Hexaplecta exhibits to Hexaplagia. Whilst in these two latter genera the six spines arise from a common central point, they arise here in two divergent groups from the two poles of a horizontal common middle rod, similar to the spicula of many Beloidea.

Spines straight and stout, six to eight times as long as the common middle rod, three-sided prismatic; in the distal half thickened, with three divergent terminal thorns; in the basal half with three to four verticils of thin lateral branches, which are again ramified, and by their united threads produce an irregular loose framework.

Dimensions.—Length of the spines 0.25, basal breadth 0.005, terminal breadth 0.02; length of the middle rod 0.03.

Spines straight and stout, three-sided prismatic, about four times as long as the common middle rod, gradually thinned towards the distal end; in the basal half with two to three verticils of forked branches, which are dichotomously ramified, and by their united threads form a loose ovate framework.

Spines straight, cylindrical, ten to twelve times as long as the common middle rod, with six to eight verticils of thorny branches, tapering towards the distal end; the branches of the verticils are simple in the distal half, again ramified in the basal half, and here connected together by irregularly branched threads forming a loose framework. (Resembles one spiculum of Sphærozoum verticillatum, Pl. 4, fig. 7, but is more richly branched, with united ramules.)

Subfamily 4. Polyplectida, Haeckel, 1881, Prodromus, p. 424.

Genus 400. Polyplecta,^[19] Haeckel.

Definition.—Plectanida with numerous (seven to nine or more) radial spines, arising from a common centre and lying in different planes.

The genus Polyplecta comprises provisionally all Plectanida possessing seven or more radial spines, united in the centre of the framework. It may be derived from Polyplagia by meeting and concrescence of the free branches. But as in the latter genus, here also the few observed species are very different, perhaps of different origin, and may be afterwards better separated as representatives of diverse genera.

Heptaplegma heptacantha, Haeckel, 1882, MS.

Seven unequal spines divergent from one common central point, slender, slightly curved, three-sided prismatic. Four spines are much larger, twice to three times as long and as thick as the three smaller spines. One of the four larger spines is directed upwards (as "apical horn"), whilst the three others diverge downwards (as "basal feet"). Each of the four larger spines bears five to seven equidistant verticils of three divergent branches, the proximal of which are branched, the distal simple. The three smaller spines lie nearly horizontally, midway between the odd apical spine and the three basal spines, and in the same meridian planes with them; each bears one verticil of three divergent branches. All the branches are united by arachnoidal threads, composing a loose wickerwork with irregular, generally quadrangular meshes.

Dimensions.—Length of the four larger spines 0.27 to 0.33, of the four smaller 0.1 to 0.14.

Enneaplegma enneacantha, Haeckel, 1881, Prodromus, p. 425.

Nine equal and equidistant, straight, cylindrical radial spines, lying nearly in one plane, arise from an irregular spongy central framework; six of them seem to be secondary, intercalated between three equidistant primary spines, which are united in the centre. (This species resembles in the nine-radial structure the remarkable Enneaphormis rotula, Pl. 57, fig. 9, and may perhaps be derived from a similar species; but it has no regular latticed shell.)

Pentaplegma decacantha, Haeckel, Prodromus, p. 425.

Ten radial spines, curved, cylindrical, irregularly branched, diverge in different directions and seem to arise in pairs from an irregular central framework, in the centre of which five primary spines are united; the latter correspond probably to the five spines of Pentaspyris, &c. The density of the spongy central framework did not allow of an accurate investigation, and makes it doubtful whether this species is not a Spongiomma.

Dimensions.—Length of the spines 0.3 to 0.4, diameter of the framework 0.18.

? Acanthodesmia polybrocha, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 368, Taf. xxvi. fig. 3.

Plegmosphæra polybrocha, Haeckel, 1881, Prodromus, p. 455.

Numerous (twenty to thirty or more) radial spines, thin, cylindrical, curved and irregularly branched, arising from an irregular central spongy framework, are connected by numerous slender arches. The specimen observed by me in 1880 in Portofino was a true Polyplecta, with three primary spines centrally united, between which numerous other spines were intercalated. The similar specimen, however, observed in 1864 in Villafranca, and figured, loc. cit., was perhaps a Plegmosphæra.

Dimensions.—Length of the radial spines 0.05 to 0.1, diameter of the framework 0.16.

Acanthodesmia dumetum, J. Müller, 1868, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. Fig. 3.

Numerous (ten to twelve or more) radial spines, thin and straight, with a few straight lateral branches, diverge in different directions and are connected by a few slender curved arches. Some similar forms, but more developed, with numerous branches and curved rods, are found in the Pacific Radiolarian ooze, and represent probably different species.

Dimensions.—Length of the radial spines 0.05 to 0.08, of the branches 0.02 to 0.03.

Habitat.—Mediterranean, French shore (Cette and Saint Tropez), Johannes Müller, surface.

Suborder III. STEPHOIDEA, Haeckel.

Stephoidea vel Stephida, Haeckel, 1881, Prodromus, p. 444.

Acanthodesmida (sensu ampliori), Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 495.

Definition.—Nassellaria without complete lattice-shell, with a skeleton composed of one or more simple rings, which may be united by a loose framework and are separated by large openings or gates. One primary or sagittal ring, determining the sagittal or median plane of the bilateral body, encloses the monaxonian central capsule.

The suborder Stephoidea, hitherto known by a few species only of "Acanthodesmida," comprises a large number of interesting Nassellaria (now more than two hundred species), which possess peculiar interest for the morphology and phylogeny of this legion. The monaxonian central capsule of the Stephoidea is surrounded either by one simple ring or by a complex system of several loosely connected rings; these may be united by a loose framework of connected branches, but never produce a complete lattice-shell, as is constantly the case in the Spyroidea, Botryodea, and Cyrtoidea. Therefore there remain between the parts of the connected rings a few large openings which we call "gates," separating them from the numerous small "pores" of the complete lattice-shells. In the most simple case, if only one ring be formed, there is also present only one "gate," the aperture of this simple ring.

The first known species of Stephoidea were observed in the Mediterranean by Johannes Müller in 1856, and described and figured in his last treatise (1858) under the names Lithocircus annularis (loc. cit., Taf. i. fig. 1) and Acanthodesmia vinculata (loc. cit., Taf. i. figs. 4-7). In the following year I myself observed two other living species in the Mediterranean, and described them in my Monograph (1862, pp. 268, 270) as Zygostephanus mülleri (Taf. xii. fig. 2) and Prismatium tripleurum (Taf. iv. fig. 6). For these four longest known Stephoidea I founded the new family of Acanthodesmida (loc. cit., p. 265), but united with them two other similar genera which I afterwards separated:—Plagiacantha (belonging to the Plectoidea) and Dictyocha (belonging to the Phæodaria).

When, in 1876, I received the rich material of the Challenger collection, I was astonished to find in it an enormous number of new, similar, and partly very interesting "Acanthodesmida," which were afterwards arranged in my Prodromus (1881, p. 444) in thirty-eight different genera and four "subfamilies," all united in one single large family, "Stephida or Monopylaria cricoidea." I retain here this natural group in the same sense, but give to it the rank of a "suborder," separating at the same time its four subfamilies as substantial "families." Since the names of the {932}latter, proposed in the Prodromus, were not quite suitable, I replace them here by the following more convenient names:—

1. Family Stephanida (= Monostephida, 1881, p. 447). Skeleton entirely formed by one simple ring (the primary vertical sagittal ring). The only "gate" is the simple aperture of the ring.

2. Family Semantida (= Dyostephida, 1881, p. 446). Skeleton composed of two rings, perpendicular to one another; the primary vertical sagittal ring bears at the base a horizontal basal ring; between the two rings two or more "basal gates remain."

3. Family Coronida (= Triostephida, 1881, p. 445). Skeleton composed of two crossed vertical or meridional rings, perpendicular to one another—the primary sagittal ring and the secondary frontal ring. Commonly the two vertical rings are united at the base by a horizontal basal ring, and between them remain two or more "basal gates."

4. Family Tympanida (= Parastephida, 1881, p. 446). Skeleton composed of two parallel horizontal rings, and upper mitral ring, and a lower basal ring, both connected by vertical or divergent columellæ, which are parts of vertical rings (primary sagittal, and secondary frontal ring).

The peculiar structure of the central capsule of the Stephoidea, and their character as true Monopylea, were first recognised by Richard Hertwig, who in 1879, in his Organismus der Radiolarien, gave an excellent detailed description of it (loc. cit., pp. 68-72, Taf. vii. figs. 4, 5). He also pointed out the near affinity of these "Acanthodesmida" with the Spyroidea or Zygocyrtida, uniting the latter with the former family.

A fuller explanation of this affinity, and of the morphological and phylogenetic importance of the "Acanthodesmida," as ancestral forms of the Spyroidea and Cyrtoidea, was given in 1882 by Bütschli (Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 495-501). He described in detail some important fossil forms of Acanthodesmida as different species of "Stephanolithis," a name which Ehrenberg had employed for various ring-like fragments of Radiolarian shells, sponges, and other fossil bodies. The four fossil species which Bütschli described represent four different genera of Stephoidea, viz., Semantis (spinescens), Semantrum (mülleri), Semantidium (haeckelii), and Tristephanium (hertwigii). On the phylogenetic conclusions, derived from these accurate observations, compare above, p. 893, &c. The topographical signification of the parts, employed by Bütschli, is contrary to mine; he calls my dorsal side the "anterior," and my ventral side the "posterior."

The geometrical fundamental form of the body in nearly all Stephoidea (with few exceptions) is distinctly bilateral or "dipleuric," so that we can easily distinguish the {933}three different dimensive axes: the principal axis with different apical and basal poles, the sagittal axis with different dorsal and ventral poles, and the lateral axis with equivalent right and left poles. In only a few genera this bilateral symmetry is not expressed, and a simpler, more regular fundamental form appears. The latter may be either primary (in the monaxonian Archicircus and Lithocircus) or secondary, afterwards acquired (in the octahedral Trissocircus and Trissocyclus, the cubical Lithocubus, the prismatic Eutympanium, and some other forms).

The most important element of the skeleton, with which the formation begins, in all Stephoidea is the simple primary or sagittal ring, lying vertically in the sagittal or median plane of the body and surrounding the monaxonian central capsule. This sagittal ring is the only essential element of the skeleton in all Stephanida, and is completely preserved in all Semantida, also in the greater part of the Coronida and Tympanida. It is partially reduced in the small groups of the true Acanthodesmida (subfamily of Coronida) and the Dystympanida and Eutympanida (subfamilies of Tympanida). Here only the vertical parts of it are preserved (dorsal and ventral rod), whilst the horizontal parts are lost (mitral and basal rod).

The sagittal ring lies constantly in the vertical median plane of the body, and therefore divides the enclosed central capsule into a right and a left half. It is rarely regular or subregular, commonly dipleuric or distinctly bilateral, so that we may easily distinguish its dorsal and ventral, apical and basal parts. The most important of these four parts or "rods" is the "basal rod" or the inferior part, because here the ring is in closer connection with the central capsule and its "porous area"; here peculiar spines or branches are commonly developed, which even on the isolated ring immediately determine the basal pole. The opposite upper part, or the "mitral rod," is also often distinguished by the peculiar appendages. The posterior part, or the "dorsal rod" (the anterior rod, a, in the description of Bütschli), is commonly more straight, often quite vertical. The opposite anterior part, or the "ventral rod" (the posterior rod, b, of Bütschli), is usually more convex, and often strongly curved or semicircular.

Whilst this dipleuric or bilateral (commonly obliquely ovate or nearly triangular) form of the sagittal ring is distinctly preserved in by far the greater number of Stephoidea, it is replaced in some few genera by a more regular, amphithect, diphragmatic, or biradial form. In this case we may often suppose a primary regularity to exist, the dorsal and ventral parts being not yet differentiated, as in Archicircus and Lithocircus, Zygostephanus and Protympanium, and perhaps also in some other forms. But in other cases the regularity is, on the contrary, secondary, being derived from original bilateral forms.

The rod of the sagittal ring is either cylindrical (with circular transverse section) or angular (commonly with triangular transverse section). In nearly all Stephoidea (with very few exceptions) branches or apophyses are developed from the ring, regularly disposed and often of great morphological importance. Commonly these {934}apophyses are developed in pairs, growing symmetrically on both sides of the ring. The most important of these apophyses are:—(1) Basal apophyses, arising from the basal hole of the ring; (2) mitral apophyses, arising from the apical pole; (3) dorsal apophyses, arising from the middle of the dorsal rod; and (4) ventral apophyses, arising from the middle of the ventral rod. The two former arise in the principal axis, the two latter in the sagittal axis of the body. Very frequently the latter pair is replaced by two pairs of transverse branches, one inferior (mandibular) and one superior (orbital). The apophyses of the ring are either simple or branched, often very large, richly ramified, and give origin to a number of further products.

Whilst in the Stephanida the primary sagittal ring alone represents the whole skeleton, it produces in all other Stephoidea one or more secondary rings. The most important of these is the horizontal basal ring, appearing first in the Semantida (Pl. 92). From the base of the sagittal ring there arise in the horizontal basal plane two pairs of lateral branches or "basal apophyses." The curved opposite branches of the corresponding pairs become united on each side of the primary ring (right and left), and so produce a second, horizontal ring, perpendicular to the former. This basal ring encloses two paired basal gates, which are enclosed on the medial side by the basal rod of the sagittal ring, and on the lateral side by two united apophyses (Semantis, Pl. 92, figs. 1, 2). These two primary basal gates are of the greatest morphological importance; we call them the "jugular gates or jugular pores" (in the description of Bütschli, the pores I, loc. cit., p. 498). The dorsal pair of basal apophyses (on their posterior edge) are the coracal rods, e (rods e of Bütschli); the opposite ventral pair (on their anterior edge) are the clavicular or furcular rods, f (rods e1 of Bütschli); compare Pls. 92-95, and their explanation.

The skeleton of Semantis, the prototype of the Semantida, thus assumes the characteristic form of a signet-ring. The basal ring enclosing the two jugular pores corresponds to the seal-plate. It is commonly more or less horizontal; but often the apophyses descend obliquely (Pl. 92, figs. 1, 2, 13, &c.), more rarely laterally (Pl. 29, fig. 11). The further development of this typical form is essentially effected by the production of new basal pores in the horizontal seal-plate. In Semantrum (Pl. 92, figs. 3, 4, 5) we find already four basal gates. Behind the jugular gates is formed a second pair, the "cardinal gates" (pores II of Bütschli). These are enclosed on the anterior margin by the coracal rods (e), on the posterior margin by the scapular rods (d), a third pair of basal apophyses, arising behind the former from the sagittal ring and uniting with them (the rods e2 of Bütschli). Commonly the two posterior, or cardinal gates are much larger than the two anterior, jugular gates. This characteristic basal plate of Semantrum, with two pairs of basal pores, is of the greatest morphological importance, as it is inherited in by far the greater number of the Nassellaria, though not so generally as Bütschli supposes. The basal ring of Semantrum is either more circular {935}or elliptical, or more polygonal, and is connected with the basal rod of the sagittal ring by three pairs of radial apophyses, the anterior furcular, the middle coracal, and the posterior scapular rods.

A third important form of Semantida is Semantidium (Pl. 92, figs. 6, 7). Here we find three pairs of basal pores in the seal-plate; the third pair, newly formed, consists of the cervical gates (e), bounded in front by the scapular rods (d), behind by a fourth pair of basal apophyses, the cervical rods.

The basal apophyses of the sagittal ring are not only of great morphological importance, because they produce by their union three typical pairs of basal gates or "collar pores," but also because their prolongations often appear as typical basal feet. The distal prolongations of the coracal rods appear in Semantiscus (Pl. 92, figs. 16-18) as two pectoral feet, those of the scapular rods as two tergal feet, whilst the opposite prolongations of the basal rod of the sagittal ring appear as two "sagittal feet" (in front an anterior or sternal, and behind a posterior or caudal foot). In the typical Cortiniscus (Pl. 92, figs. 11-13) only three feet are developed; an odd caudal and two paired pectoral feet (compare above, p. 891). The typical basal ring of the Semantida, with its paired basal gates (Semantis), reappears in the majority of the Coronida, differing from the former in the development of a second vertical ring, which lies in the frontal plane (perpendicular to the sagittal ring), and which we therefore call the frontal ring. In only one small group of the Coronida the basal ring is absent, namely, in the Zygostephanida, and here the frontal ring appears in the simplest form, as a complete elliptical meridian ring, crossing the sagittal ring perpendicularly on the two poles of the main axis (Zygostephanus, Pl. 93, figs. 1-4), Four large lateral gates between the two rings remain open. This form may be derived directly from the Stephanida in the following way; from both poles of a simple sagittal ring there arise two opposite lateral apophyses, which in the frontal plane become curved one towards the other, and united in the poles of the transverse axis. The basal apophyses would be the coracal rods. But it is also possible that Zygostephanus was derived from Semantis by the loss of the furcular rods.

The three typical rings (or the "dimensive rings") of the Stephoidea appear in their most complete form in the subfamily Trissocyclida (Pl. 93, figs. 7, 13). Here all three rings are undivided and completely developed in the three dimensive planes, perpendicular one to another. Between them there remain eight large open gates; the four superior are the four "lateral gates" of Zygostephanus, the four inferior are the four basal gates of Semantrum. The four latter are originally much smaller than the four former; but in Trissocircus and Trissocyclus (Pl. 93, figs. 10-12) they reach the same size. Therefore all eight gates are here of equal form and similar size, and the basal ring, now a true equatorial ring, divides the two meridional rings into two equal halves.

In the Eucoronida, a third subfamily of Coronida, the sagittal and the basal rings {936}are complete, but the frontal ring is incomplete, its basal part being wanting (Pl. 82, figs. 4-6). Therefore we find here six large gates between the three rings; four upper lateral gates (between the two crossed vertical rings) and two lower basal gates (between the basal rod of the sagittal ring and the two halves of the basal ring). Eucoronis, the type of this subfamily, may be derived either directly from Semantis by development of a frontal ring, or from Tristephanium by loss of the basal part of the frontal ring.

A quite simple basal ring with a single gate, distinguishes the fourth subfamily of Coronida, the Acanthodesmida (sensu restricto), the genera Coronidium (Pl. 82, figs. 1, 2, 7, 8) and Acanthodesmia (Pl. 93, fig. 5). The horizontal basal ring alone is here complete, whilst both vertical rings (the sagittal and frontal rings) are incomplete, their basal parts being wanting. Therefore there are here five gates, four lateral and one basal. These forms may be derived from Eucoronis by loss of the basal rod of the primary sagittal ring.

The Tympanida, the fourth family of Stephoidea, exhibit another type of ring structure. Here two parallel horizontal rings are constantly developed, one on the apical pole, the other on the basal pole of the sagittal ring. The latter is the same basal ring as in the Semantida and Coronida. The former is a "mitral ring," developed in the same manner, by union of two pairs of horizontal lateral branches, which arise on both sides from the apical rod (or mitral rod) of the sagittal ring. In the simplest case these two parallel horizontal rings are connected only by the sagittal ring, which is either complete (Protympanium, Pl. 93, fig. 14) or incomplete (Parastephanus, Pl. 93, fig. 21). But commonly also an incomplete frontal ring is present, so that the two horizontal rings are connected by four vertical or subvertical rods; two of these "columellæ" are the dorsal and ventral rods of the sagittal ring, the two others are the lateral rods of the frontal ring. Between the former and the latter are sometimes developed two, four, or more accessory columellæ (probably halves of accessory incomplete diagonal meridian rings). In this way arise the characteristic "drum-forms" of many Tympanida, in which the two parallel horizontal rings correspond to the upper and lower rings of a drum, whilst the connecting vertical columellæ correspond to its parallel lateral rods (Pl. 83, figs. 1, 2, &c.).

Originally the two horizontal rings of these "drum-shells" are both bisected by the complete sagittal ring, each provided with two lateral gates (Protympanida). But in the Eutympanida both rings exhibit one simple gate only, the apical and the basal rod of the sagittal ring being lost. In the Paratympanida both rings are closed by a secondary lattice-plate whilst in the Dystympanida the upper (mitral) ring alone is closed by such a plate, the lower (basal) ring is open. In some Eutympanida the shell assumes the strange form of a regular geometrical cube, the twelve edges of which are represented by thin rods of silex (Lithocubus)—its four upper edges represent the mitral ring, the four lower the basal ring; two opposite of the four vertical {937}cube-edges are the lateral halves of the frontal ring, the two other alternate ones are the remaining halves of the reduced sagittal ring (dorsal and ventral rod) (Pl. 82, fig. 12).

In many Tympanida and Coronida a loose irregular lattice or framework is developed, which partly closes the large open gates. But this never reaches the completeness of a true lattice-shell, such as we find in the Spyroidea, Botryodea, and Cyrtoidea. In by far the greater number of Stephoidea the corners, and partly also the rods, of the shell are armed with numerous irregular spines, often forked or richly branched. Among these spines the descending "basal apophyses" possess a peculiar importance, since by their regular number and disposition they correspond to the radial rods of the Plectoidea, and to the typical "feet" of the Spyroidea and Cyrtoidea. The most important of them are the three cortinar feet (one caudal and two pectoral) of Cortina, Cortiniscus, &c. (compare above, p. 891).

The Central Capsule exhibits in the Stephoidea the same characteristic structure as in all other Monopylea, first exactly pointed out by Richard Hertwig in 1879 (Organismus der Radiol., p. 71, Taf. vii. figs. 4, 5). Its form is commonly ovate or ellipsoidal, sometimes also lentelliptical or nearly spherical. It exhibits constantly on the basal pole the porochora or porous area, and in the basal half the podoconus or pseudopodial cone. From the surrounding sagittal ring it is separated by a thick jelly-like calymma, which commonly exhibits numerous zooxanthellæ. The numerous pseudopodia are commonly branched, with rather rare anastomoses. The membrane of the central capsule is thick.

Synopsis of the Families of Stephoidea.

Family XLVIII. Stephanida, Haeckel (Pl. 81).

Monostephida, Haeckel, 1881, Prodromus, p. 447.

Definition.—Stephoidea with a simple sagittal ring, without any lattice-work.

The family Stephanida is the most simple of all Stephoidea, and probably the common ancestral group of this suborder (compare above, p. 933). The skeleton {938}consists of a simple ring only, surrounding the central capsule, and armed commonly with simple thorns or with larger branched spines. The branches of these spines are constantly free, never joining together. Therefore the shell exhibits no trace of fenestration or lattice-work, no pores or gates, except the simple large gate of the ring itself. In all other Stephoidea we find secondary gates or lattice-work.

The first known form of this family is Lithocircus annularis, described by Johannes Müller in 1858 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1). He observed already the central capsule ("Blase") surrounded by the circular ring of silex, and the calymma ("Strahlige Gallert") enveloping the whole body. The peculiar structure of the soft body, particularly the "area porosa" on the basal pole of the central capsule, and the pseudopodial cone within it, were first accurately described by Hertwig (in 1879). A great number of simple rings, similar to these, were found in the Challenger collection, and are here arranged in six genera and forty-eight species.

The simple ring of silex, which alone forms the skeleton of the Stephanida, corresponds to the primary or sagittal ring of the other Stephoidea, and lies therefore vertically in the median or sagittal plane of the body. We can therefore distinguish on it four different segments, rods or bows, two of which are more horizontal, two more vertical. The former are one upper bow or apical rod, and one lower bow or basal rod. The latter are one posterior bow or dorsal rod, and one anterior bow or ventral rod. Sometimes each of these four component bows is distinguished by a corner-spine, or by a pair of divergent branches.

In the two simplest (and probably oldest) genera of Stephanida, in Archicircus and Lithocircus, the dorsal and ventral rods of the ring are equal and cannot be distinguished; therefore the fundamental form is here amphithect, diphragmatic, or biradial (the poles of the sagittal axis being equal). In the four other genera the dorsal rod is more straight (often vertical) and more or less different from the ventral, convexly curved rod; therefore the fundamental form is here dipleuric or bilateral, as in the greater number of all Nassellaria (the poles of the sagittal axis being unequal). The general form of the ring in this latter case is commonly obliquely ovate or nearly triangular, the basal pole being more pointed, the apical pole more rounded (Pl. 81).

The rods or bows of the ring are either roundish or cylindrical (with circular or elliptical transverse section), or they are prismatic or angular (commonly with triangular transverse section). In the latter case one edge usually is prominent in the sagittal plane (on the convex outside of the ring), whilst two other edges diverge laterally on both sides of it. The inner or concave margin of the ring is commonly smooth.

The inner perimeter of the large gate, enclosed by the ring, is commonly rounded (elliptical or ovate), rarely angular. However, the outer perimeter of the ring is {939}nearly always polygonal, with prominent corners, and usually from these arise thorns or branched spines which are regularly disposed. Regarding this disposition we may distinguish three cases: A, the spines lie in the sagittal plane and form a single row, arising from the median edge; B, the spines lie on both sides of the latter and form two parallel rows, arising from the two lateral edges; C, the spines represent a combination of A and B, and are disposed in three rows, two paired rows arising from the two lateral edges, and an odd middle row between them, arising from the median edge. The spines are simple, without branches, in Archicircus and Zygocircus; more or less branched in Lithocircus and Dendrocircus. The branches are often richly ramified or arborescent, and exhibit great variety in size, special form, and direction (compare Pl. 81).

The number and disposition of the spines or groups of spines are usually constant, and may be employed in the further progress of our knowledge, to distinguish a number of genera and subgenera. Very commonly (perhaps in the majority of the Stephanida) we find six groups of spines, an apical group on the upper rod of the sagittal ring, a basal group on the lower rod (on the porochora of the central capsule), two ventral groups on the anterior rod, and two dorsal groups on the posterior rod. In other species we find four or eight groups instead of six, and sometimes a larger number.

The most important of these apophyses of the ring are the basal spines, arising from its basal pole, where the porochora of the central capsule rests upon it. They are often much larger and more branched than the other spines, and attain a peculiar morphological value in the small subfamily Cortinida. Here we find three or four regularly disposed "basal spines," which may be compared to the typical "basal feet" of the Cyrtellaria, appearing in the majority of Spyroidea and Cyrtoidea. Cortina, one of the most important Nassellaria, bears three typical divergent feet on the base of the simple ring, two paired anterior or "pectoral feet," and an odd posterior or "caudal foot." The latter appears as a direct basal prolongation of the dorsal rod of the ring, and is opposed to an upper prolongation of the same, which corresponds to the "apical horn" of the Cyrtellaria (Pl. 97, figs. 1-3). As already explained above, these three basal feet of Cortina possess the highest phylogenetic value, since they may also be compared with the three primary radial spines of the Plectoidea, and so connect the Cyrtellaria and the Plectellaria. Stephanium differs from Cortina in the possession of four basal feet, an odd anterior or "sternal foot" being added to the three typical feet of the latter (Pl. 92, figs. 20, 21). Some forms of Plectoidea (Plagoniscus, Plectaniscus, &c.) seem to be nearly related to these Cortinida, and may be easily transformed into them by development of a complete ring, embracing the central capsule. They seem to demonstrate the near affinity of all these triradiate Nassellaria (Pl. 91, figs. 4, 5, 9, 10).

Synopsis of the Genera of Stephanida.

Subfamily 1. Lithocircida, Haeckel.

Genus 401. Archicircus,^[20] n. gen.

Definition.—Stephanida with a simple amphithect or diphragmatic ring, smooth or thorny, without branched spines and basal feet.

The genus Archicircus is the most primitive and simplest form of all Stephoidea, and probably the common ancestral form, not only of this suborder, but of the greater number of all Nassellaria (compare above, p. 893). The skeleton consists only of a quite simple sagittal ring, in which commonly a slight difference of both poles of the main axis (basal and apical pole) is visible, but no difference between the dorsal and the ventral bow of the ring. In my Prodromus (1881, p. 447) the species of Archicircus were disposed partly in the subgenus Monostephus, partly in the genus Lithocircus.

Subgenus 1. Monostephus, Haeckel, 1881, Prodromus, p. 447.

Gate circular. Ring circular, smooth, its transverse section also circular. The simplest form of all Stephoidea.

Dimensions.—Diameter of the gate 0.05 to 0.08; thickness of the ring 0.006 to 0.008.

Gate circular. Ring circular, with three elegantly denticulate edges (one outer median and two lateral edges). Transverse section of the ring triangular.

Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.008.

Gate elliptical. Ring elliptical, on the inner margin smooth, on the outer margin with fifteen to twenty equal, short, simple, or slightly forked thorns. Transverse section ovate.

Dimensions.—Diameter of the gate 0.05 to 0.09; thickness of the ring 0.01 to 0.014.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.

Gate ovate. Ring elliptical, smooth, with three prominent, slightly distorted edges, without thorns; in the transverse section triangular.

Dimensions.—Diameter of the gate 0.08 to 0.12; thickness of the ring 0.006 to 0.009.

Gate ovate. Ring ovate, thorny, with three distorted edges, in the transverse section triangular; surface covered with numerous simple small thorns arising from the three edges.

Dimensions.—Diameter of the gate 0.1 to 0.15; thickness of the ring 0.01 to 0.012.

Subgenus 2. Archistephus, Haeckel.

Definition.—Ring polygonal, with four to six or more prominent corners (and commonly with simple spines arising from the corners).

Gate square. Ring square, with three edges and four short simple pyramidal spines on the four corners, opposite in pairs in two perpendicular diameters. Transverse section triangular.

Gate rhombic. Ring rhombic, with four prominent edges and four pairs of short, divergent, pyramidal spines on the four corners, arising from the lateral edges of the four rods, about as long as the radius of the gate.

Dimensions.—Diameter of the gate 0.04 to 0.08; thickness of the ring 0.007 to 0.01.

Gate square or rhombic. Ring rhombic, with three prominent edges and twelve stout and straight pyramidal spines, about as long as the radius of the gate. In each of the four corners are three divergent spines, arising from the three edges of each two meeting rods.

Gate ovate. Ring hexagonal, with three prominent edges and six short pyramidal thorns at the six corners; the basal thorn is either simple or forked.

Gate subregular, hexagonal. Ring hexagonal, with three sharp edges and six equal radial pyramidal spines, arising from the six corners and placed in the plane of the ring, about as long as the diameter of the gate.

Lithocircus annularis, R. Hertwig (non J. Müller), 1879, Organismus der Radiol., p. 69. Taf. vii. fig. 5.

Gate hexagonal, with prolonged main axis. Ring hexagonal, with two prominent edges and six pairs of equal, short, conical spines, arising from the two edges of the six rods at the six corners and divergent on each side of the plane of the ring. The basal spine-pair is doubled, therefore there are in all fourteen spines.

Dimensions.—Diameter of the gate 0.05 to 0.07; thickness of the ring 0.005 to 0.006.

Gate ovate. Ring hexagonal, with three prominent edges and twenty-two to twenty-four simple curved spines, arising from the six corners and about as long as the diameter of the gate. In the basal corner arise six to nine larger spines, protecting the basal pole of the central capsule. From each of the five other corners arise three spines, diverging from the three edges.

Dimensions.—Diameter of the gate 0.07 to 0.11; thickness of the ring 0.008 to 0.011.

Gate hexagonal or subcircular. Ring hexagonal, with two sharp prominent edges and six pairs of divergent spines, about as long as the radius of the gate, and arising from the two edges at the six corners. The two apical and the two basal spines are simple and conical, whilst the eight other spines, arising in pairs from the two dorsal and the two ventral corners, are slightly forked.

Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.015.

Genus 402. Lithocircus,^[21] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Definition.—Stephanida with a simple amphithect or diphragmatic ring, armed with branched spines, without typical basal feet.

The genus Lithocircus is the oldest known form of all Stephoidea, founded by J. Müller in 1856 for his Lithocircus annularis, the first species of this suborder described. We retain here this cosmopolitan form as the typical representative of the genus, which differs from the preceding Archicircus, its ancestral form, in the development of branched radial spines.

Lithocircus annularis, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1.

Gate circular. Ring circular, with four forked or simply branched spines, opposite in pairs in two diameters, perpendicular one to the other. Spines with slender curved fork-branches, about as long as the diameter of the gate. The specimen figured by J. Müller bears a supernumerary fifth spine; numerous other specimens observed by me exhibited a regular cross of four spines.

Dimensions.—Diameter of the gate 0.1 to 0.15; length of the spines 0.01 to 0.18.

Gate square. Ring square, with three sharp denticulate edges, and four large bunches of richly branched spines on the four corners. In each corner arise three curved spines, about as long as the diameter of the ring; their numerous irregular branches are forked and curved like the antlers of deer.

Gate elliptical. Ring pentagonal, with three prominent edges and five pairs of branched spines on the five corners. In each corner arise two or three curved spines, about as long as the radius of the gate, each with two to four forked branches.

Gate elliptical. Ring hexagonal, with three prominent edges and six pairs of branched spines, arising from the six corners. Each of the twelve spines is short and stout, only half as long as the radius of the gate, and bears a bunch of ten to twenty short, densely aggregated, conical or horn-like curved branches.

Gate elliptical or subcircular. Ring hexagonal, with three wing-shaped distorted edges and six groups of branched spines, arising from the six corners. In each corner arise three short and stout divergent spines, each bearing a bunch of numerous short roundish branches like a cauliflower, scarcely as long as the thickness of the ring.

Dimensions.—Diameter of the ring 0.1 to 0.12, length of the spines 0.01 to 0.02.

Gate circular. Ring hexagonal, with three sharp edges and six pairs of large branched spines, arising from the flat lateral edges on the six corners. Each of the twelve spines is horizontally expanded, longer than the diameter of the ring and dichotomously forked like the antlers of a {945}reindeer. If the lateral ends of the branches of this species become united in the frontal plane, we get Microcubus, the four upper spines forming the mitral ring, the four middle the equatorial ring, and the four lower the basal ring.

Gate ovate. Ring ovate, with three sharp prominent edges. The two lateral edges are smooth. The median edge (in the sagittal plane) bears sixteen to twenty forked spines (commonly eight dorsal, eight ventral, and four basal). All the spines are of nearly equal size, slightly curved, and about half as long as the short sagittal axis of the ring.

Dimensions.—Diameter of the gate 0.08 to 0.12; length of the spines 0.03 to 0.04.

Gate ovate or nearly elliptical. Ring ovate, with three prominent edges, and numerous richly branched spines arising from the three edges. The specimen figured, which I observed living in the Mediterranean, exhibited eight bunches of larger spines, three dorsal, three ventral, one apical, and one basal bunch; the latter much larger than the seven others. Each bunch was composed of two to four larger and numerous smaller spines, their branches curved and forked. The ovate purple central capsule, with a distinct podoconus, filled more than the half of the gate.

Dimensions.—Diameter of the gate 0.1 to 0.13; length of the spines 0.05 to 0.15.

Habitat.—Mediterranean (Portofino, 1880), Atlantic (Canary Islands), Station 354, surface.

Genus 403. Zygocircus,^[22] Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 496.

Definition.—Stephanida with a simple dipleuric or bilateral ring, smooth or thorny, without branched spines and basal feet.

The genus Zygocircus and the following Dendrocircus differ from the two preceding older genera in the bilaterally symmetrical or dipleuric form of the sagittal ring. Whilst in Archicircus and Lithocircus the two sagittal halves or bows of the ring, the dorsal and ventral bow, are equal (therefore the fundamental form amphithect or diphragmatic), here both bows become distinctly different; the dorsal bow is constantly more straight (often vertical), the ventral bow more convex (obliquely ascending). This dipleuric differentiation is most important, as it is transmitted to the greater number of Nassellaria by heredity.

Gate ovate. Ring half ovate or nearly triangular, with three curved edges and three prominent corners, one apical and two basal protuberances. Dorsal rod vertical, twice as long as the horizontal basal rod. Ventral rod convexly curved.

Dimensions.—Diameter of the gate 0.05 to 0.07; height of the tubercles 0.01 to 0.015.

Gate triangular. Ring triangular, with three curved edges and three prominent corners, which are prolonged into nine divergent conical spines; three spines arising from the three edges of each corner. Dorsal rod vertical; ventral and basal rods curved and convergent.

Dimensions.—Diameter of the gate 0.11 to 0.13; length of the spines 0.01 to 0.015.

Gate ovate. Ring quadrangular, without edges, with four simple conical spines of different sizes; one smaller apical, one larger basal, and two equatorial spines of middle size (one dorsal and one ventral). Dorsal and ventral rod curved.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.018 to 0.026.

Gate rhombic. Ring rhombic, with three prominent edges, and eight short conical curved spines arising from the lateral edges at the four corners of the rhombus. The basal and ventral spine are larger than the apical and dorsal spine; the ventral rod is more curved (with smaller angle) than the shorter dorsal rod. The medial edge of the ring is smooth, without spines.

Gate roundish pentagonal. Ring very thick (about as thick as the radius of the gate), irregularly pentagonal, with prominent sagittal edge. On both sides of the latter arise at the five corners five pairs of short simple irregularly curved spines. The four ventral spines are larger than the four dorsal, and the two basal spines larger than the eight former, forked. (In fig. 8 the basal spines are turned upwards.)

Gate irregularly hexagonal. Ring obliquely hexagonal, thick, without edges, with six short and stout conical spines on the six corners. The two spines of the curved ventral rod are longer than the two spines of the straight dorsal rod. The apical spine is smaller and the basal spine larger than the four others.

Dimensions.—Diameter of the gate 0.07 to 0.09; length of the spines 0.01 to 0.03.

Gate obliquely ovate. Ring obliquely hexagonal, with three sharp edges and three short conical spines on each of the six corners. Therefore each hexagonal edge bears six short radial spines of equal size.

Dimensions.—Diameter of the gate 0.04 to 0.08; length of the spines 0.01 to 0.02.

Gate semicircular. Ring semicircular or irregularly hexagonal, without edges, with twelve short blunt spines, arising in pairs from the six corners; two apical, two basal, and between them two equatorial corners. Three pairs of spines remain on the straight dorsal rod, three on the curved ventral rod.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.01 to 0.02.

Gate obliquely ovate. Ring semi-ovate, with straight dorsal and curved ventral rod, partly with distorted edges. Six bunches of numerous short and straight conical spines arise from the ring, one larger bunch (often trifid) from the apex, two smaller bunches from the dorsal, two from the ventral rod, and one very large bunch from the base. The six bunches are often more separated, smaller, and the spines shorter than in the figured specimen, which passes over into Dendrocircus.

Dimensions.—Diameter of the gate 0.12 to 0.16; length of the spines, 0.01 to 0.07.

Gate irregularly roundish or ovate. Ring irregularly polygonal or sometimes nearly circular, without edges, armed with a single series of ten to fifteen short pyramidal spines, which are irregularly {948}disposed in the sagittal plane. The ventral rod is strongly curved, often semicircular, the dorsal rod less curved or nearly straight.

Dimensions.—Diameter of the gate 0.05 to 0.07; length of the spines 0.004 to 0.02.

Zygocircus productus, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497.

Gate obliquely ovate. Ring irregularly roundish, semi-ovate or ovate, with interrupted and distorted edges, and with a large number (ten to twenty or more) of simple, irregularly formed and asymmetrically disposed spines; commonly some larger spines at the base.

Dimensions.—Diameter of the gate 0.05 to 0.09; length of the spines 0.005 to 0.02.

Zygocircus productus, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi p. 496.

Lithocircus productus, R. Hertwig, 1879, Organismus d. Radiol., p. 69, Taf. vii. fig. 4.

Gate obliquely ovate. Ring obliquely ovate, with three complete prominent edges and with numerous (ten to twenty or more) simple, short conical spines, arising in three series from the three edges; commonly some smaller spines at the base.

Dimensions.—Diameter of the gate 0.1 to 0.2; length of the spines 0.005 to 0.02.

Genus 404. Dendrocircus,^[23] Haeckel, 1881, Prodromus, p. 447.

Definition.—Stephanida with a simple dipleuric or bilateral ring, armed with branched spines, without typical basal feet.

The genus Dendrocircus has the same dipleuric or bilaterally symmetrical form of the sagittal ring as its ancestral genus Zygocircus. It differs from the latter in the development of branched radial spines, and therefore bears to it the same relation as the amphithect Lithocircus does to the simpler Archicircus.

Gate irregularly quadrangular or nearly semicircular. Ring quadrangular, edgeless, with four unequal sides; ventral rod more curved and with longer sides than the dorsal rod. From the four edges arise four strong, irregularly branched spines, about as long as the diameter of the gate, {949}with curved branches; the ventral and basal spines larger than the dorsal and apical spines. Similar to Lithocircus quadricornis (Pl. 81, fig. 9), but less branched, and with a striking difference between the shorter dorsal and the longer ventral rod.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.05 to 0.07.

Gate obliquely ovate. Ring irregularly quadrangular, with three prominent edges. From the latter arise at the four corners twelve divergent, irregularly branched spines (three in each corner), about as long as the radius of the gate, with curved branches; the three basal spines larger than the nine others.

Dimensions.—Diameter of the gate 0.08 to 0.1; length of the spines 0.04 to 0.06.

Gate obliquely ovate or nearly elliptical. Ring irregularly ovate, with three distorted edges and six pairs of branched spines. The two ventral pairs are much more distant than the two dorsal pairs, the ventral rod being longer and more curved than the dorsal rod. All twelve spines are of nearly equal size, are more or less curved, about as long as the diameter of the gate, and each bears six to twelve irregular short branches at the end.

Dimensions.—Diameter of the gate 0.07 to 0.08; length of the spines 0.05 to 0.08.

Gate irregularly roundish or nearly circular. Ring of the same form, with slight edges and six pairs of elegant arborescent spines (one apical, two dorsal, two ventral, and one basal pair); the three latter somewhat larger than the three former. Each tree is larger than the ring, in the basal half simple, in the distal half forked, each fork-branch with numerous dichotomous terminal branches.

Dimensions.—Diameter of the gate 0.06 to 0.08; length of the spines 0.12 to 0.15.

Gate irregularly ovate. Ring thick, ovate, with three denticulate edges and six bunches of stout, branched and spinulate, curved spines. The four ventral spines are more distant than the four dorsal, the ventral rod being more curved than the dorsal. The latter bears above the two apical spines. The two basal spines are much larger, deeply forked; their four fork-branches may be compared to the four basal feet of Stephanium.

Dimensions.—Diameter of the ring 0.09 to 0.11; length of the spines 0.03 to 0.06.

Gate irregularly ovate or nearly semicircular. Ring of the same oblique form, thick, with interrupted and distorted edges, armed with eight to twelve larger irregularly formed and branched acute spines; between them numerous conical smaller spines. This common species is very polymorphous and variable.

Dimensions.—Diameter of the ring 0.05 to 0.08; length of the spines 0.005 to 0.02.

Gate obliquely ovate. Ring irregularly ovate or roundish, very thick, without edges, armed with numerous (eight to twelve or more) short and stout branches, which are shorter than the diameter of the gate, irregularly disposed and branched, with very numerous clustered blunt ramules.

Dimensions.—Diameter of the gate 0.07 to 0.09; length of the spines 0.02 to 0.06.

Subfamily 2. Cortinida, Haeckel.

Genus 405. Cortina,^[24] n. gen.

Definition.—Stephanida with a simple dipleuric or bilateral ring, bearing at the base three divergent feet (one odd caudal and two paired lateral feet).

The genus Cortina and the following Stephanium represent together the small but very important group of Cortinida, differing from the simple Lithocircida in the possession of three typical basal feet, which are transmitted to the majority of the Nassellaria by heredity, and produce their peculiar triradial structure. They appear therefore as a combination of the simple ring (Zygocircus) with three basal feet (Plagonium). One of these three divergent feet is the odd caudal foot, opposite to the apical horn; the two others are the paired lateral or pectoral feet. (On the probable origin and the typical signification of Cortina compare above, pp. 891-894.)

Ring ovate, smooth, or with a few short thorns. Apical horn oblique, curved, simple, smooth, about as long as the sagittal axis of the ring. Feet divergent, curved, simple, smooth, about as {951}long as the horn; the caudal foot shorter than the two pectoral feet. Very variable in form and size.

Dimensions.—Height of the ring 0.06 to 0.09, breadth 0.04 to 0.06; length of the feet 0.05 to 0.1.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and in various depths.

Ring kidney-shaped or nearly semicircular, with revolute vertical dorsal rod and strongly curved ventral rod; both rods with two pairs of spine-bunches. Apical horn nearly straight, thorny, longer than the ring, directed a little obliquely backwards. Feet slightly curved, of equal length, two to three times as long as the ring; each armed with few large bunches of curved spines, which are more developed in the caudal foot than in the two pectoral feet.

Dimensions.—Height of the ring 0.14, breadth 0.08; length of the feet 0.2 to 0.3.

Ring subcircular, smooth. Apical horn and the three divergent feet of equal size and similar form, cylindrical, straight, about as long as the ring, at the distal end thickened, with a dimply cone (similar to Tripospyris conifera and Tripospyris eucolpa, Pl. 84, figs. 4, 7).

Ring elliptical, with three forked horizontal spines (one on the dorsal and two on the ventral rod). Apical horn and the three divergent feet of equal size, somewhat longer than the ring, slightly curved, in the distal half forked.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms. Fossil in Barbados.

Ring ovate, with six pairs of branched horizontal spines, three on the dorsal and three on the ventral rod. Apical horn very large, arborescent, about as long and as broad as the ring. Feet similar to the horn, also richly branched, of equal size. All the rods and their branches curved, with prominent distorted edges.

Dimensions.—Height of the ring 0.13 to 0.17, breadth 0.1 to 0.12; length of the feet 0.15 to 0.2.

Ring ovate, with four pairs of forked horizontal spines (two dorsal and two ventral pairs). Apical horn straight and stout, as long as the ring, with trifid point. Three feet equal, widely divergent, very large, branched like a deer's antler, with very numerous short and stout, curved and pointed branches. All rods and branches roundish, without edges.

Dimensions.—Height of the ring 0.1, breadth 0.07; length of the feet 0.12 to 0.16.

Genus 406. Stephanium,^[25] n. gen.

Definition.—Stephanida with a simple dipleuric or bilateral ring, bearing at the base four divergent feet (two sagittal and two lateral feet).

The genus Stephanium differs from the preceding nearly allied Cortina in the production of four basal feet; the new foot, missing in the latter, is the anterior or sternal foot. Therefore Stephanium may be regarded as the archetype of all those Nassellaria in which, on the base of the sagittal ring, there are developed four typical feet—two sagittal feet (the posterior caudal and anterior sternal foot) and two lateral feet (right and left). On the origin of Stephanium compare above, p. 893, &c.

Ring ovate, with three prominent dentate edges and a short pyramidal apical horn. Four feet all of nearly equal size, about as long as the ring, also with three thorny edges, in the upper half divergent, in the lower convergent.

Dimensions.—Height of the ring 0.12, breadth 0.08; length of the feet 0.11 to 0.13.

Ring elliptical, without edges, thorny, with a stout, thorny apical horn of the same length. Four feet curved and irregularly branched, divergent, of different size. The two sagittal feet (the anterior sternal and posterior caudal) about as long as the ring. The two lateral feet (right and left) nearly twice as long, more richly branched.

Dimensions.—Height of the ring 0.16, breadth 0.11; length of the feet 0.15 to 0.3.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms. Fossil in Barbados.

Family XLIX. Semantida, n. fam.

Definition.—Stephoidea with a single vertical ring (the primary sagittal ring), bearing on its base a horizontal ring (basal or cortinar ring) with two to four or more basal gates (or cortinar pores).

The family Semantida differs from the preceding Stephanida in the development of a small horizontal ring on the base of the primary vertical sagittal ring. By the crossing of these two rings a small latticed basal plate is formed, with one or two pairs of pores; rarely with a greater number of "basal pores." The production of this characteristic "basal plate" is of the greatest morphological importance, as the beginning of the numerous different lattice-formations, which are differentiated in the great majority of Nassellaria.

In my Prodromus (1881, p. 446) I had enumerated the Semantida with three genera (Nos. 298 to 300) as a separate subfamily of the Dyostephida or "Stephoidea biannularia," and characterised these "Dyostephanida" by the following definition: "Skeleto annulis duobus composito, qui in duobus planis invicem perpendicularibus jacent; altero annulo (sagittali) verticali, altero (basali) horizontali." As the names there given were already employed with another signification, and as the Zygostephanida (there united with the Dyostephanida) are more closely related to the Coronida, I now change the names, and propose to call the family Semantida, expressing by this term the typical similarity of the skeleton to a signet-ring (Semantis, Semantrum, Semantidium).

At about the same time, some Stephoidea of this family were accurately described by Bütschli (1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 495, Taf. xxxii. figs. 6, 7, 8). He called them Stephanolithis, a name which Ehrenberg had employed, not for complete shells of Radiolaria, but for isolated parts of such, and for siliceous fragments of different skeletons, needles of Sponges, &c. The three species described by Bütschli represent three different genera of our Semantida, viz., Semantis spinescens (with two gates in the basal plate), Semantrum mülleri (with four gates), and Semantidium haeckelii (with six gates). He pointed out the great morphological value of the fenestrated basal plate and its paired gates, as beginnings of numerous other Nassellaria. But his opinion, that in all Spyroidea and Cyrtoidea, derived from these, two pairs of basal gates were constant, was erroneous, nor was the formation of the first pair naturally explained; he supposed that the formation of the basal plate begins by development of an odd sagittal apophysis, arising from the base of the primary sagittal ring. But this odd sagittal apophysis ("der unpaare mediane Kieselfortsatz c1", loc. cit., p. 497) is in reality not a primary {954}and essential part of the skeleton, but secondary and of little morphological value, absent in the majority of the Semantida and of the other Nassellaria.

We divide our family Semantida into two different subfamilies, which possibly possess a direct phylogenetic relation to the two subfamilies of Stephanida:—The Semantiscida have no typical feet, and have arisen directly from the Lithocircida; the Cortiniscida, however, possess the three typical basal feet of Cortina, and may therefore be derived directly from the Cortinida. Since these three cortinar feet are probably identical with the three primary radial rods of the Plectoidea, an immediate affinity also to these Nassellaria is indicated.

The Semantiscida, which do not possess these three basal cortinar feet, are the simpler forms of the family. The simplest of all, and perhaps the common ancestral form of the whole family, is Semantis (Pl. 92, figs. 1, 2). It may be derived from Archicircus or Zygocircus by development of two pairs of horizontal apophyses on its base, around the porochora of the central capsule. The two rods of each side (right and left), becoming curved one towards the other, and meeting laterally, form a simple horizontal gate, and the two paired basal gates together, a horizontal ring or basal ring, to which the primary sagittal ring is perpendicular. In the next allied genus, Semantrum (Pl. 92, figs. 3-5), three pairs of horizontal apophyses are developed, and therefore two pairs of basal gates produced, an anterior and a posterior. In the third genus, Semantidium (Pl. 92, figs. 6, 7), three pairs of basal pores or gates are visible, surrounded and separated by four pairs of horizontal apophyses, which arise from the base of the sagittal ring. Finally, in Clathrocircus (Pl. 92, figs. 8-10) the number of apophyses is much increased, and two parallel rows of pores are developed along the two sides of the sagittal ring.

The basal plate or the "seal," developed from the base of the primary sagittal ring or "signet-ring," is therefore a horizontal ring, which becomes bisected by the latter, and exhibits either one pair of primary "basal gates" or two or three pairs of these important basal pores, rarely more. Since these pores possess the greatest morphological value, and are probably everywhere homologous, we give to them and to the separating apophyses certain names, and call the anterior pair of gates, "jugular pores" (i in our figures, the pair I of Bütschli); the middle (usually the largest) pair, "cardinal pores" (k in our figures, the pair II of Bütschli), and the posterior, smaller pair, "cervical pores," l. The typical pairs of rods, by the union of which these basal pores arise, are the following:—(1) the clavicular or furcular rods, f, the first pair (rods e1 of Bütschli), (2) the coracal rods, e, between the jugular and cardinal pores (rods e of Bütschli), (3) the scapular rods, g, between the cardinal and cervical pores (rods e2 of Bütschli), (4) the cervical rods, the fourth pair of apophyses, the most posterior, h. Bütschli supposes that the topographical succession of the three typical pairs of basal pores is also the chronological succession, the jugular being formed first, the {955}cardinal second and the cervical pores third but it seems that this succession is often altered and that the cardinal pores (the largest), appear first, the jugular pores (in front of them) second and the cervical pores third (or perhaps sometimes in the inverse succession).

The Cortiniscida, the second subfamily of Semantida, differ from the preceding Semantiscida in the possession of three typical basal feet, which are probably inherited from the Cortinida, and perhaps indirectly from the Plagonida (Plagoniscus). The simplest and the most important form of this second family is Cortiniscus (Pl. 92, figs. 11-13), differing from its probable ancestral form, Cortina, in the development of a basal ring, produced by horizontal union of the basal apophyses. The three typical feet are the same as in all triradiate Nassellaria, two paired pectoral feet (p₁, p₁₁) diverging on the anterior base of the sagittal ring, whilst the odd caudal foot (c) lies on its posterior base in the sagittal plane and appears as a basal prolongation of the dorsal rod of the sagittal ring; the upper part of the dorsal rod is usually prolonged into an ascending apical horn. In Stephaniscus (Pl. 92, figs. 14, 15) four basal feet are visible, an anterior or sternal foot (z) being added as a prolongation of the basal rod of the ring, opposite to the caudal foot. Finally, Semantiscus (Pl. 92, figs. 16-18) is distinguished by the possession of six divergent basal feet, probably identical with those of all six-radiate Nassellaria; three of these may be regarded as primary and perradial, the odd caudal and the paired pectoral feet; the three other intercalated as secondary or interradial feet, the odd sternal (z) and the paired tergal feet (t₁, t₁₁).

The basal plate of these Cortiniscida exhibits the same important differences as in the preceding Semantiscida, either one, or two, or three pairs of basal gates being developed. But there occur also in some species (mainly in Cortiniscus) only three basal gates, an odd anterior (between the two pectoral feet and a connecting horizontal bar), and two paired posterior (between the two pectoral and the odd caudal foot). It requires further accurate researches to solve the important problem, what the true homologies of these typical basal pores and the separating bars are in the different genera of Semantida. In Semantiscus there are three pairs of basal pores in the horizontal seal, corresponding to those of Semantidium and the radial rods or bars between, these are the basal parts of the six radial feet; therefore the odd caudal foot (t) seems to be the posterior, and the odd sternal foot (z) the anterior prolongation of the basal part of the primary sagittal ring; the two paired anterior or pectoral feet (p₁, p₁₁) the prolongations of the coracal rods (e) and the two paired posterior or tergal feet (t₁, t₁₁), the prolongations of the scapular rods (g). But it is not yet certain whether these six radial feet and the separating gates of the basal plate are all the same and truly homologous in all six-radiate Nassellaria. In every case the comparative study of the Semantida is of the highest value for the accurate knowledge of the Monopylea.

Synopsis of the Genera of Semantida.

Subfamily 1. Semantiscida, Haeckel.

Genus 407. Semantis,^[26] n. gen.

Definition.—Semantida with two basal pores (or jugular pores), without typical basal feet.

The genus Semantis, the most primitive and the oldest of the Semantida, is of the greatest morphological interest, as the first form of Stephoidea which produces gates or pores by communicating branches, and therefore the probable ancestral form not only of this family, but of the greater number of all Stephoidea, and perhaps even of all Spyroidea and Cyrtoidea. Semantis arises from Archicircus by the production of two pairs of lateral branches from the basilar rod of the sagittal ring, one anterior pair of clavicular rods, and one posterior pair of coracal rods. By junction of the clavicular and coracal rod on each side arises a left and a right pore, the "jugular pore or jugular gate."

Sagittal ring obliquely ovate, nearly trapezoidal, with six pairs of short mammillated knobs or branches; dorsal rod straight, vertical, with two pairs of knobs, ventral rod strongly convex, also with {957}two pairs of knobs; two other pairs in the apical rod. Basilar rod horizontal, straight. Basal ring with six pairs of similar knobs, three on each side. Basal gates ovate or nearly triangular.

Sagittal and basal ring nearly of the same form as in the preceding species, but half as thick and armed with numerous branched spines which are about half as long as the diameter of the main gate, and with thin and curved pointed branches.

Sagittal ring kidney-shaped, very thick, with six pairs of short, thorny, or irregularly tuberculated knobs (two dorsal, two apical, and two ventral pairs). Basal ring smooth, scarcely half as thick, horizontal, with two semicircular basal gates, about half as broad as the main gate. From the two opposite lateral corners of the basal ring two slender upwardly curved spines arise, resembling the basal part of a commencing frontal ring.

Sagittal ring elliptical, with four pairs of stout arborescent spines (two apical and two equatorial pairs), which are irregularly branched and forked, with numerous thin lateral branches. Apex with a short conical trifid vertical horn. Basal ring thorny, with obliquely descending slightly curved bars.

Sagittal ring thin, semicircular, smaller than the thin basal ring, which exhibits two semicircular gates. Both rings are armed with numerous small spines of equal size, which on the former are arranged in two, on the latter in three regular rows. (The basal rod of the sagittal ring, separating the two basal gates, in fig. 3 is, by mistake, not distinctly enough drawn.)

Stephanolithis spinescens, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p.160, Taf. i. fig. 29.

Stephanolithis spinescens, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497, Taf. xxxii. figs. 7a, 7b.

Sagittal ring ovate with four pairs of thin, irregularly branched spines, two apical pairs, one on the straight dorsal rod and one on the curved ventral rod. Basilar rod with a posterior and an anterior forked rod (commencing caudal and sternal foot). Basal ring square, with two lateral spines, and two triangular gates scarcely one-third as broad as the ring-gate. An internal ascending procolumna (rod c₁ in the figure of Bütschli) connects the basal and ventral rods of the sagittal ring.

Genus 408. Semantrum,^[27] n. gen.

Definition.—Semantida with four basal pores (two anterior jugular and two posterior cardinal pores), without typical basal feet.

The genus Semantrum, one of the most important of the Nassellaria, arises from the preceding Semantis by duplication of the two basal gates. Behind the pair of coracal rods there arises from the basilar rod of the sagittal ring a third pair of lateral horizontal branches, the scapular rods. These become connected with the coracal rods on each side, and so produce a second posterior pair of basal pores, the "cardinal gates." These are constantly larger than the anterior "jugular gates." Therefore the vertical ring of Semantrum possesses a horizontal basal ring with four very characteristic gates, enclosed by three pairs of lateral curved and connected branches, and these become transmitted by heredity to the majority of the Nassellaria.

Sagittal ring subcircular or ovate, with three edges and four sagittal forked spines on the odd edge (two dorsal and two ventral spines). Basal ring decagonal, with ten simple or forked spines on the ten corners. Jugular gates tetragonal. Cardinal gates pentagonal.

Sagittal ring semicircular, thorny, without edges. Basal ring tetragonal or nearly cordate, with a small anterior and a large posterior bow-shaped incision; on the lateral edges with numerous irregular thorns. Jugular gates pear-shaped. Cardinal gates nearly kidney-shaped.

Sagittal ring elliptical, tuberculate. Basal ring trapezoidal, also with roundish thick rods and small irregular tubercles on the margin. Jugular gates ovate, two-thirds as broad as the triangular cardinal gates.

Stephanolithis mülleri, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi pp. 499, 539, Taf. xxxii. figs. 8a, 8b, 8c.

Sagittal ring nearly semicircular or obliquely ovate, thorny. Basal ring also nearly semicircular, with two slight sagittal incisions (one anterior and one posterior), on the lateral edges with numerous small thorns. Jugular pores (pair I of Bütschli) pear-shaped. Cardinal pores (pair II of Bütschli) triangular. Sometimes (but not constantly) a pair of cervical bows connects the scapular bars with the subvertical dorsal rod of the sagittal ring.

Sagittal ring circular, smooth. Basal ring also nearly circular and smooth; its four basal gates of nearly equal size, elliptical or subcircular; the jugular pores scarcely smaller than the cardinal pores. All rods smooth, cylindrical, without edges and thorns.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms; also fossil in Barbados.

Sagittal ring triangular, with vertical straight ascending dorsal rod, horizontal straight basilar rod and obliquely ascending, slightly curved ventral rod; all rods nearly cylindrical, with irregular {960}branched thorns and distorted edges. Jugular pores triangular, scarcely half as broad as the large semicircular cardinal pores.

Sagittal ring obliquely ovate, thorny. Basal ring kidney-shaped or nearly pentagonal, with broad concave dorsal incision and five larger branched spines on the five corners; between them smaller thorns. Jugular gates pear-shaped, scarcely half as broad as the triangular cardinal gates.

Genus 409. Semantidium,^[28] n. gen.

Definition.—Semantida with six basal pores (two anterior jugular, two middle cardinal, and two posterior cervical pores), without typical basal feet.

The genus Semantidium exhibits a further developmental stage of the basal plate of the Semantida. Whilst this plate in Semantis possesses one pair of basal pores, and in Semantrum two pairs, here in Semantidium it has three pairs. The new third pair is produced on the dorsal edge of the basal plate, which becomes connected with the basal part of the dorsal rod of the sagittal ring by a pair of cervical rods. The middle pair of pores (the cardinal) are always larger than the anterior (jugular) and the posterior (cervical pores). The same form of basal plate is preserved in numerous Spyroidea and Cyrtoidea, as a "cortinar septum with six collar pores," (e.g., Pl. 53, fig. 18).

Sagittal ring ovate, thorny. Basal ring rhombic or nearly square, with four short conical descending spines on the four prominent edges (two sagittal and two lateral); between them numerous smaller irregular thorns. Jugular and cervical gates nearly equal, ovate, half as broad as the triangular cardinal gates between them.

Sagittal ring ovate, with six pairs of short branched thorns (two apical, two dorsal, and two ventral). Basal ring hexagonal, with three pairs of short branched thorns on the six corners (one {961}sagittal pair, one posterior and one anterior). All six gates of the basal plate triangular, the jugular and cervical a little smaller than the cardinal gates.

Stephanolithis Haeckelii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 538, Taf. xxxii. figs. 6a, 6b.

Sagittal ring elliptical, with three pairs of short horizontal branched spines, one apical and two equatorial pairs (one dorsal and one ventral). Basal ring roundish hexagonal, with numerous short thorns on the margin. Jugular pores ovate, about half as broad as the ovate cardinal pores and twice as broad as the small cervical pores.

Sagittal ring semicircular, thorny; basal ring pentagonal, with short spines on the margin and five stronger thorny spines on the five corners. Jugular pores ovate, smaller than the triangular cervical pores. Cardinal pores two to three times as large as each of the former, pentagonal.

Genus 410. Clathrocircus,^[29] Haeckel, 1881, Prodromus, p. 447.

Definition.—Semantida with a variable number of pores on the apical and the basal part of the ring, symmetrically arranged, without typical basal feet.

The genus Clathrocircus comprises those Semantida in which the sagittal ring bears not only basal pores (as in the three preceding genera) but also apical pores (on the opposite pole of the main axis), or a variable number of pores along the whole ring. All these pores are symmetrically arranged in pairs. In the simplest form there are only two apical pores opposite to four basal pores, whilst in the highest state of development the whole ring bears two complete circles of pores. At both poles of the transverse axis two large lateral gates remain open. If these become closed by lattice-work, Clathrocircus passes over into Dictyospyris.

Sagittal ring circular, smooth, with three pairs of pores (one apical and two basal). The two apical pores are triangular with two lateral spines, and correspond to the two mitral gates of the Tympanida. The four basal pores form a hexagonal basal plate, with six lateral spines, and correspond to the four basal pores of Semantrum; the two jugular are pear-shaped, and half as broad as the two triangular cardinal pores.

Sagittal ring elliptical, smooth, with four pairs of pores (two apical and two basal). The four apical pores are of nearly equal size, subcircular, and form a regular cross around the apical pole. The four basal pores are ovate, and form a quadrangular plate, armed with marginal thorns; the two jugular pores are somewhat smaller than the two cardinal pores.

Sagittal ring ovate, thorny, with five pairs of pores (two apical and three basal). The four apical pores are roundish and form a cross. The six basal pores are triangular and form a hexagonal plate with thorny margin; the two jugular pores are somewhat larger than the two cervical, and half as broad as the two cardinal pores.

Sagittal ring ovate, smooth, with six pairs of pores (two apical and four basal). The four apical pores are of nearly equal size and form a quadrangular mitral plate with two large lateral horns. The eight basal pores are of very different size (the four central far larger than the two anterior and the two posterior), and form a hexagonal basal plate, also with two large lateral horns. The four branched lateral horns (two upper and two lower) form together an incomplete frontal ring.

Sagittal ring ovate, thorny, with eight pairs of pores. The four apical and the four basal pores are elliptical and far larger than the four dorsal and the four ventral pores. Resembles a Dictyospyris with open lateral gates.

Sagittal ring circular, smooth, with ten to twelve pairs of roundish pores, forming together a complete lattice-girdle with two parallel circular rows of pores. Four larger of these are the four gates of the basal ring (two jugular and two cardinal pores).

Subfamily 2. Cortiniscida, Haeckel.

Definition.—Semantida with large, typical, regularly disposed basal feet (originally three cortinar feet, one odd caudal and two paired pectoral).

Genus 411. Cortiniscus,^[30] n. gen.

Definition.—Semantida with three typical basal feet (an odd caudal foot and two paired lateral or pectoral feet).

The genus Cortiniscus is of peculiar importance, as the common ancestral form of the Cortiniscida, or those Semantida in which the basal ring is provided with typical, regularly disposed basal feet—three, four, or six. Since these typical basal feet (or "cortinar feet") are preserved in the greater number of all Nassellaria, determining their triradial structure, they possess a great morphological value. Cortiniscus exhibits the same three primary feet as Cortina, from which it differs in the production of two or more basal pores (between the odd caudal and the paired lateral feet).

Sagittal ring ovate, thorny, with three prominent, distorted edges; its dorsal rod nearly straight and vertical, with one or two pairs of short thorns; its ventral rod strongly curved, with three or four pairs of divergent thorns. Basal ring larger than the sagittal ring, with two semicircular gates and obliquely ascending halves, which on the inner and lower edge are smooth, {964}on the outer and upper thorny. Apical horn and the three divergent feet nearly equal, straight, about as long as the sagittal ring, with three thorny edges.

Sagittal ring nearly semicircular, with prominent distorted edges and six pairs of small roundish papillate tubercles (three pairs on the straight dorsal, three on the curved ventral rod). Apical horn short and stout, with a tuberculate knob. Basal ring smaller than the sagittal ring with two elliptical gates. Three feet short and stout, irregularly branched like a cauliflower, with numerous short papillate tubercles.

Sagittal ring elliptical, smooth. Apical horn conical, smooth. Basal ring larger than the sagittal ring, with three elliptical gates of equal size; two paired, posterior (jugular pores) between the basal parts of the caudal foot and the two pectoral feet, and an odd, anterior (sternal pore) between the basal parts of the two pectoral feet and a connecting horizontal convex sternal bow.

Sagittal ring elliptical, with four pairs of short branched thorns, two posterior on the straight dorsal, and two anterior on the curved ventral rod. Basal ring smaller than the sagittal ring, with four triangular gates; the two anterior (jugular pores) a little smaller than the two posterior (cardinal pores). Apical horn and the three divergent feet shorter than the sagittal ring, irregularly branched, with curved, often tuberculate branches.

Sagittal ring ovate, thorny, with three distorted edges; dorsal rod nearly straight and vertical prolonged upwards into a stout thorny apical horn, downwards into the caudal foot. Basal ring smaller than the sagittal ring, with four elliptical or nearly triangular gates; the two anterior (jugular pores) about half as large as the two posterior (cardinal pores). Three feet of equal size, thorny, divergent, straight or slightly curved, about as long as the diameter of the sagittal ring.

Genus 412. Stephaniscus,^[31] n. gen.

Definition.—Semantida with four typical basal feet (two sagittal and two lateral or pectoral feet).

The genus Stephaniscus differs from the preceding Cortiniscus in the production of a fourth (sternal) foot, and therefore exhibits the same relation to it that Stephanium among the Stephanida bears to Cortina. It differs from Stephanium, in the production of a basal ring, with pores or gates between the bases of the basal feet. Two of these feet are sagittal (the posterior caudal and the anterior sternal foot), whilst the other two are lateral or pectoral (right and left). The basal lattice-plate exhibits either two pores ("jugular gates") or four pores (two anterior jugular and two posterior cardinal gates).

Sagittal ring nearly circular, smooth, with a short conical apical horn. Basal ring square, smooth, with two triangular gates. Four feet simple, equal, conical, divergent, about as long as the diameter of the ring.

Sagittal ring subcircular, thorny with a small thorny apical horn. Basal ring also nearly circular, with two large semicircular gates and a few small thorns. All four feet curved and forked, the fork-branches again ramified, with numerous short curved and pointed branches. The two lateral feet (right and left) are larger and more branched than the two sagittal feet (sternal and caudal foot).

Sagittal ring oblique, ovate, with three prominent thorny edges; its dorsal rod nearly straight and vertical, the ventral rod strongly curved; apex with a small curved horn. Basal ring with a few short thorns and four gates of different size; the two anterior (jugular pores) ovate or nearly triangular, two-thirds as broad as the two posterior subcircular or pentagonal (cardinal pores). All {966}four feet simple, curved, with three edges, the posterior (caudal) foot larger, the anterior (sternal) foot smaller than the two lateral (pectoral) feet.

Sagittal ring elliptical, thorny, with a larger apical horn. Basal ring nearly square, with short marginal thorns and four large ovate gates of nearly equal size. All four feet of equal size divergent, curved, irregularly branched, with short curved branches.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms. Fossil in Barbados.

Genus 413. Semantiscus,^[32] n. gen.

Definition.—Semantida with six typical basal feet (two sagittal, two pectoral, and two tergal feet).

The genus Semantiscus may be the archetype of those Nassellaria which exhibit six typical basal feet, in combination with the sagittal ring. Three of these are the primary feet of Cortina and Cortiniscus, the other three are secondary productions between the former. The basal ring may possess either two, four, or six basal pores.

Sagittal ring elliptical, with a large branched apical horn. Basal ring small, square, with two small triangular gates (or jugular pores). From its periphery there arise six short and stout cylindrical feet, one very large (caudal) from the posterior corner, two tergal on each side, two opposite (pectoral) from the lateral corners, and one odd sternal from the anterior corner. All six spines bear a bunch of ten to twenty stout pointed conical branches, partly simple, partly forked.

Sagittal ring semicircular, broad, latticed, with two pairs of irregular dorsal and two pairs of ventral pores. The dorsal rod is straight and vertical, prolonged upwards into a short serrate apical horn, downwards into a straight linear caudal foot. The ventral rod is curved and prolonged into a similar sternal foot. Basal ring hexagonal, with four ovate gates (two smaller jugular and two larger cardinal pores); its four lateral corners prolonged into four curved thorny lateral feet (two {967}anterior larger pectoral, and two posterior smaller tergal feet). This species may be regarded as a commencing Hexaspyris or Liriospyris.

Sagittal ring ovate, thorny, with a small apical horn. Basal ring with six roundish or nearly triangular gates; the two jugular pores are smaller than the two cardinal and larger than the two cervical pores. The separating bars between these six pores are prolonged into six straight, thorny widely divergent feet; three larger feet (the caudal and the two pectoral) with a pair of apophyses, three smaller between them simple (the sternal and the two tergal feet).

Family L. Coronida, Haeckel.

Triostephida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Stephoidea with two crossed vertical rings, perpendicular one to the other (the primary sagittal and the secondary frontal ring). Usually their common base bears a horizontal basal ring, but a mitral ring (or a horizontal ring at the apex) is never developed.

The family Coronida comprises those Stephoidea in which the primary sagittal ring (of the Stephanida and Semantida) becomes crossed by a second vertical ring, the lateral or frontal ring. Between these two vertical meridian rings, perpendicular to one another, four large apertures remain constantly open, the "lateral" gates. But besides these four constant openings, usually (excepting only in the Zygostephanida) other gates are developed on the common base of the two crossed rings, produced by a third, horizontal, basal ring. These basal gates are the same which we have found already in the Semantida.

The distinction of the Coronida from the other Stephoidea is always easy. In the Stephanida and Semantida, the frontal ring, or the second meridian ring, which we find in all Coronida, is never developed. On the other hand these latter never exhibit the typical "mitral ring," or the second, upper, horizontal ring, which distinguishes the Tympanida.

We distinguish here, among the Coronida, four different subfamilies, which perhaps afterwards may be better separated as families. Of these four groups the Zygostephanida and Acanthodesmida exhibit the nearest relationship to the Stephanida, whilst the Eucoronida and Trissocyclida possess a closer affinity with the Semantida.

The Zygostephanida, constituting the first subfamily, exhibit four large gates only, and differ from all other Coronida in the absence of a basal ring and of basal gates. Therefore the skeleton is entirely composed of two crossed vertical rings, perpendicular to one another; the first is the primary or sagittal ring (inherited from the Stephanida), the second is the new lateral or frontal ring. The four large lateral gates are either quite simple (Zygostephanus) or partly closed by loose and irregular lattice-work (Zygostephanium). The Zygostephanida may be derived directly from the Stephanida by development of lateral branches forming a frontal ring. They commonly possess the same characteristic spines or branches, and the same typical difference between the straight dorsal rod and convex ventral rod of the sagittal ring, which we found in the greater number of Stephanida. The frontal ring is commonly elliptical or kidney-shaped, and much larger than the ovate sagittal ring.

The Acanthodesmida, forming the second subfamily of Coronida, differ from all other members of this family in the possession of a large simple basal gate, surrounded by a simple horizontal basal ring. Only this ring is complete, whilst the two crossed vertical meridian rings (the primary sagittal and the secondary frontal ring) are incomplete, both truncated at the base by the basal ring. Therefore there remain here between the three rings five large gates (recognised previously by Johannes Müller in 1856 in Acanthodesmia): four lateral gates (the same as in the Zygostephanida) and one central basal gate. The latter is always quite simple and serves for the emission of the pseudopodia, arising from the basal pole of the central capsule. The four lateral gates are either quite simple (Coronidium) or partly closed by irregular loose lattice-work (Acanthodesmia). The subfamily Acanthodesmida may be derived either directly from the Stephanida (by development of a central basal gate) or from the Eucoronida (by loss of the basilar part of the sagittal ring).

The Eucoronida, the third subfamily, are the most important group of the Coronida; their numerous species are much more frequent and more widely distributed than those of the other three subfamilies. They may be derived immediately from the Semantida by the development of a lateral or frontal ring. This remains incomplete in the basal part, whilst the two other rings, perpendicular to it (the vertical sagittal ring and the horizontal basal ring), are complete. Therefore the shell constantly exhibits six large open gates between the three rings; four lateral gates (the same as in the Zygostephanida and Acanthodesmida) and two basal gates (inherited from Semantis); the latter correspond to the "jugular pores" of the Spyroidea and Cyrtoidea; they remain constantly simple. The four lateral gates may also remain simple (Eucoronis) or they may become partly closed by irregular loose lattice-work (Plectocoronis). The remarkable genus Podocoronis is distinguished by the development of typical descending basal feet, which are regularly disposed and correspond to the typical "cortinar feet" of the other Nassellaria. There may be developed either two lateral feet (as lower {969}prolongations of the segments of the frontal ring), or three feet (one caudal and two pectoral, as in Cortina and Cortiniscus), or four feet (two sagittal and two lateral, as in Stephanium and Stephaniscus), or six feet (two sagittal, two pectoral, two tergal, as in Semantiscus), sometimes numerous feet (as in Petalospyris and Anthocyrtis, &c.).

The Trissocyclida represent the fourth and last subfamily of Coronida, distinguished from all others in the possession of three complete rings, perpendicular one to another, and of eight large gates separated by them. Two of the three rings are vertical (the primary sagittal and the secondary frontal ring), the third is horizontal (the basal ring). The four upper gates correspond to the four lateral gates of the preceding three subfamilies; the four lower gates are the same as the four basal gates of Semantrum (two primary jugular and two secondary cardinal gates); therefore the Trissocyclida may be derived directly from these Semantida by development of a complete frontal ring. Probably the two jugular gates were originally smaller than the two cardinal, but usually they have become equal. In Tristephanium (the common ancestral form of the Trissocyclida) and in the closely allied Tricyclidium the four basal gates remain smaller than the four lateral gates. But in two other genera, Trissocircus and Trissocyclus, the four lower or basal gates reach the same size as the four upper or lateral gates; therefore all eight gates become equal and the basal ring becomes equatorial. In the most regular species of the latter genera also the three rings become perfectly equal and cannot be any longer distinguished. Here the original bilateral (or dipleuric) fundamental form of the shell passes over into a regular cubic or octahedral form (with three equal, isopolar axes, perpendicular one to another). The eight large gates of the Trissocyclida usually remain simple (Tristephanium, Trissocircus), but sometimes they become partly closed by loose lattice-work (Tricyclidium, Trissocyclus).

The original rings, and the secondary rods or bars, composing the loose framework of the Coronida are either roundish (with circular or elliptical transverse section) or three-edged (with triangular transverse section), rarely quadrangular or provided with distorted edges. The branches or spines arising from them, are either simple or branched, and offer a great variety in number, form, and disposition. The most important forms are those which develop the three typical basal feet of Cortina, e.g., Podocoronis cortina (Pl. 97, fig. 2).

The Central Capsule of the Coronida is the same as in the other Stephoidea (comp. p. 937), and offers all those characteristic peculiarities of "Monopylea" which we have mentioned above in the general description of the Nassellaria (p. 890). Usually it is spherical or ellipsoidal, often violin-shaped or bilobed, with a sagittal constriction. The porochora of its basal pole is in close contact with the base of the sagittal ring.

Synopsis of the Genera of Coronida.

Subfamily 1. Zygostephanida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with four large lateral gates, without basal gate. Skeleton composed of two complete vertical rings, perpendicular one to another—the primary sagittal and the secondary frontal ring.

Genus 414. Zygostephanus,^[33] Haeckel, 1862, Monogr. d. Radiol., p. 268.

Definition.—Coronida with four large, simple, lateral gates, without basal gate and lattice-work. Skeleton composed of two simple meridional rings, perpendicular to one another.

The genus Zygostephanus, founded by me in 1862 for the Mediterranean Zygostephanus mülleri, is the simplest and most primitive of all the Coronida, and may {971}therefore be regarded as the common ancestral form of this family. The simple skeleton is composed of two meridional rings only, perpendicular one to another—a sagittal and a frontal ring.

Subgenus 1. Zygostephus, Haeckel, 1881, Prodromus, p. 446.

Definition.—The two vertical rings of nearly equal height, therefore without sagittal constriction.

Both rings elliptical, of nearly equal height, smooth, without spines. Frontal ring somewhat longer than the sagittal. No sagittal constriction.

Both rings elliptical, of nearly equal height, with a serrate prominent edge on the outer convexity (in the transverse section three-edged). No sagittal constriction.

Zygostephanus mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 268, Taf. xii. fig. 2.

Both rings elliptical, of nearly equal height, armed with numerous (about fifty) slender curved spines, as long as the radius of the rings; commonly each ring with twelve pairs of divergent spines. No sagittal constriction.

Both rings elliptical, of nearly equal height, armed with numerous branched spines, which are arranged on each ring in two divergent rows; the branches of the spines are curved and partly protect the open gates. No sagittal constriction.

Subgenus 2. Zygostephaniscus, Haeckel, 1881, Prodromus, p. 446.

Definition.—The two vertical rings of different heights; the frontal ring higher than the sagittal ring, therefore with a sagittal constriction in the median plane.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction, armed with numerous irregular short spines. Sagittal ring thicker and lower, only two-thirds as high, with four pairs of short divergent spines (two ventral and two dorsal pairs).

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction, armed with numerous irregular spines, which are partly simple, partly branched. Sagittal ring thicker and lower, only half as high, with a few short conical spines at the apical and basal poles.

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction; its two halves pentagonal. Between numerous smaller spines there arise from the frontal ring six groups of larger branched spines, two odd in the corners of the highest points (curved like two horns), two branched pairs on the prominent lateral corners (at right and left), and two pairs in the corners of the lowest points (like four branched basal feet). Sagittal ring only two-thirds as high, with four pairs of irregular spines.

Genus 415. Zygostephanium,^[34] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with four large, partly latticed, lateral gates, without basal gate. Skeleton composed of two meridional rings perpendicular to each other.

The genus Zygostephanium differs from the preceding ancestral genus Zygostephanus in the development of lattice-work along the two crossed rings, produced by their anastomosing branches. Therefore the four large lateral gates between them, which are quite simple, in the preceding genus here become more or less fenestrated.

Tympaniscus dizonius, Haeckel, 1882, Manuscript.

Both rings elliptical, of nearly equal height, smooth, without spines. Sagittal ring with four pairs of small pores (two apical pairs and two basal pairs). Frontal ring with three pairs of small pores (one pair lateral, one pair above and one pair below).

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction. Sagittal ring ovate, about two-thirds as high as the frontal ring. Both rings three-edged, armed with numerous short and branched bristle-shaped spines, which anastomose along their three edges and produce two series of irregular polygonal pores.

Frontal ring violin-shaped, concave on the upper and lower margins, with a deep sagittal constriction. Sagittal ring ovate, about two-thirds as high as the frontal ring. Both rings covered with numerous branched irregular spines, which partly anastomose along the edges of the rings, and produce small irregular polygonal pores.

Subfamily 2. Acanthodesmida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with five large gates (four lateral and one basal). Skeleton composed of three rings, perpendicular one to another, two of which are vertical and incomplete (the primary or lateral, and the secondary or frontal), the third is horizontal and complete (the tertiary or basal ring).

Genus 416. Coronidium,^[35] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with five large simple gates (four lateral and one basal). Skeleton composed of two incomplete meridional rings and one complete basal ring, without lattice-work.

The genus Coronidium and the following, nearly allied Acanthodesmia, form together the peculiar subfamily of Acanthodesmida—not in the wider sense in which I first founded this group (1862, Monogr. d. Radiol., p. 265), but in the restricted sense, which is exactly defined in my Prodromus (1881, p. 445). According to this definition, the shell is composed of three different rings, perpendicular to one another; only one of these is complete, the simple horizontal basal ring; the two others are incomplete and vertical (the primary or sagittal and the secondary or frontal ring). Therefore there remain constantly between the three rings five characteristic large openings or gates; four of these are lateral (between the halves of the two meridional rings), the fifth is basal, enclosed by the horizontal basal ring. The longest known type of this subfamily is Acanthodesmia vinculata, the five characteristic gates of which are clearly distinguished by its discoverer, Johannes Müller ("Das Gehäuse besteht nur aus den Leisten zwischen fünf grossen Lücken"). The Acanthodesmida may be derived from the Eucoronida by reduction of the basilar rod of the sagittal ring. If in Eucoronis this basal rod be lost, Coronidium arises.

Frontal ring elliptical, with few scattered thorns, twice as broad as high, and three times as broad as the smooth rhombic basal ring. Sagittal ring semicircular, very stout, twice as thick as the two other rings, with short lateral thorns (in the figure seen from the apical pole, which exhibits a four-lobed dimple). Basal gate rhombic.

Frontal ring kidney-shaped, one and a half times as broad as high, with a slight sagittal constriction. Sagittal ring ovate, smaller, about of the same size as the elliptical basal ring. Rods of all three rings cylindrical, bearing numerous short and stout curved spines, partly simple, partly branched. Four bunches of larger spines on the four corners of the basal ring, and one very large bunch on the apical pole. Basal gate elliptical, one and a half times as broad as long.

Frontal ring kidney-shaped, twice as broad as high, one and a half times as broad as the elliptical basal ring, both with a slight sagittal constriction. Sagittal ring ovate. All three rings {975}(in the figure seen from the apical pole) with cylindrical rods, armed with numerous stout spines, branched like a deer's antler. Basal gate rather oblong, twice as broad as long.

Frontal ring and sagittal ring nearly circular, of equal size, truncated at the base. Basal ring circular, somewhat smaller. All three rings with prominent edges, bearing bunches of short and straight pointed spines, like those of an Acacia. Basal gate circular.

Genus 417. Acanthodesmia,^[36] J. Müller, 1856, Monatsber. d. k. preuss.

Definition.—Coronida with five large, partly latticed gates (four lateral and one basal). Skeleton composed of two incomplete, partly fenestrated meridional rings, and one complete basal ring.

The genus Acanthodesmia, the oldest known form of all Coronida, differs from the preceding Coronidium, its ancestral form, in the development of irregular loose lattice-work along the rings, and therefore bears to it the same relation that Zygostephanium does to Zygostephanus. The first species described by Johannes Müller, Acanthodesmia vinculata ("with five large gates between the bars of the shell") remains the true type of this genus; the second species described by him (Acanthodesmia dumetum) belongs to the Plectanida (Polyplecta).

Acanthodesmia vinculata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. figs. 4-6 (non 7).

Lithocircus vinculatus, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Frontal ring violin-shaped, one and a half times as broad as high, with a sagittal constriction. Sagittal ring ovate, smaller. The four gates between the two rings are partly fenestrated by a few thin threads, irregularly branched and connecting the two rings. A few short thorns are scattered here and there. Basal gate elliptical.

Frontal ring violin-shaped, one and a half times as broad as high, with a deep sagittal constriction. Sagittal ring semicircular, half as high as the frontal ring. The four gates between the two rings are partly fenestrated by anastomosing branches of the numerous, irregularly branched spines, which cover all three rings. Basal gate nearly circular, smaller than the sagittal ring.

Frontal ring kidney-shaped, nearly twice as broad as high, with a flat sagittal constriction. Sagittal ring semicircular. The four gates between the two rings are partly fenestrated by an arachnoidal network, composed of thin, irregularly branched threads, arising from the rings. The edges of all three rings are armed with irregular thorns. Basal gate circular, larger than the sagittal ring.

Frontal ring kidney-shaped with a deep sagittal constriction. Sagittal ring ovate. The four gates between the two rings irregularly fenestrated, with a few large polygonal meshes. Edges of the rings with a few scattered thorns. Basal gate violin-shaped.

Subfamily 3. Eucoronida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large gates (four lateral and two basal gates). Skeleton composed of three rings perpendicular to one another, two of which are complete (the vertical sagittal, and the horizontal basal ring); the third is incomplete (the vertical frontal ring).

Genus 418. Eucoronis,^[37] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large simple gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without typical feet.

The genus Eucoronis and the following two nearly allied genera (Plectocoronis and Podocoronis) compose together the important subfamily Eucoronida. In this typical main group of Coronida the shell is constantly composed of three rings and six gates. The vertical sagittal ring and the horizontal basal ring are complete (as in the Semantida); the vertical frontal ring is incomplete. Between these three rings remain six large open gates, the four upper (or lateral) are always much larger than the four lower (or basal gates). Eucoronis may be derived from Semantis by development of the frontal ring.

Subgenus 1. Acrocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Rings smooth or rough, armed with numerous short spines or thorns.

Frontal ring elliptical, twice as broad as high, with a slight constriction at the apical pole, armed with three pairs of short conical spines, one apical pair (near the constriction) and two lateral pairs (one upper and one lower pair). Sagittal ring of the same height, half the breadth and double the thickness, also armed with three pairs of spines (one basal, one dorsal, and one ventral pair).

Frontal ring elliptical, smooth, one and a half times as broad as high, without sagittal constriction, with horizontal basal gates. Sagittal ring of the same height and thickness, also elliptical and smooth. No spines on either of the smooth rings.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with a sagittal constriction (often much deeper than in the specimen figured). Sagittal ring ovate, about two-thirds as high as the frontal ring. Rods of both rings without edges, cylindrical, armed with numerous short conical thorns.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface and at various depths.

Frontal ring violin-shaped, twice as broad as high, on the upper and the lower margin concave, with a deep sagittal constriction. Sagittal ring pentagonal, with straight horizontal basal rod, two-thirds as high as the frontal ring. Rods of both rings with sharp prominent edges, bearing numerous short pyramidal spines.

Subgenus 2. Lithocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Rings armed with numerous large, branched or arborescent spines.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with sagittal constriction. Sagittal ring ovate, two-thirds as high as the frontal ring. Both rings armed with numerous stout spines, irregularly branched like a deer's antler. (Very similar to Coronidium cervicorne, Pl. 82, fig. 1, which I formerly confounded with it, but differing in the complete sagittal ring, which in the latter form is incomplete and has lost its basal part.)

Frontal ring kidney-shaped, with a deep sagittal constriction in the concave basal part. Sagittal ring ovate, half as high as the frontal ring. Both rings armed with numerous thin, richly branched and arborescent spines (branches much thinner and more numerous than in the preceding and following species).

Lithocoronis challengeri, Haeckel, 1881, Prodromus, p. 445.

Frontal ring violin-shaped, one and a half times as broad as high, with a strong sagittal constriction. Sagittal ring nearly circular, two-thirds as high as the frontal ring. Both rings armed with numerous irregularly branched spines. (The specimen figured, with red central capsule and numerous xanthellæ, was observed living by me at the Canary Islands.)

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and at various depths.

Genus 419. Plectocoronis,^[38] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large, partly latticed gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without developed typical feet.

The genus Plectocoronis differs from the preceding Eucoronis, its ancestral form, in the development of loose irregular lattice-work along the two meridional rings, and therefore bears to it the same relation that Acanthodesmia does to Coronidium. If the lattice-work become more complete and close the gates, these Coronida pass over directly into Spyroidea (Zygospyrida).

Basal ring and frontal ring elliptical, without sagittal constriction. Sagittal ring ovate. The frontal and sagittal rings are bordered on both edges with an incomplete series of small irregular pores. All three rings smooth, without spines.

Basal ring and frontal ring nearly circular, without sagittal constriction. Sagittal ring elliptical, prolonged at the apex into an apical horn from which two branched lateral bows descend and unite with the uppermost parts of the frontal ring. Four other small bows descend from the lowermost parts of the latter and unite with the basal ring. From the lateral corners of the basal ring descend two short vertical feet. (May be regarded as derived from Podocoronis toxarium, Pl. 83, Fig. 7, by development of the bows connecting the rings.)

Basal ring and frontal ring kidney-shaped, with deep sagittal constriction. Sagittal ring ovate, prolonged at the apex into an oblique horn. From the edges of the angular rings delicate threads arise, which anastomose and form irregular arachnoidal meshes, partly closing the four open lateral gates. Two basal gates simple. From the four nodal points of the basal ring there arise four, short diverging feet, comparable to rudimentary cortinar feet (two lateral from the frontal ring and two sagittal from the primary ring, as basal prolongations).

Genus 420. Podocoronis,^[39] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring provided with typical, regularly disposed, descending feet (cortinar feet).

The genus Podocoronis differs from the two preceding nearly allied genera in the development of typical radial feet on the basal ring, which by their regular disposition and their general appearance among the Spyroidea and Cyrtoidea obtain great morphological importance. According to the different number and disposition of these basal feet (or "cortinar feet"), the following subgenera may be distinguished (regarded in my Prodromus, 1881, p. 445, as separate genera):—Dipocoronis with two lateral feet, Tripocoronis with three cortinar feet (most important!), Tetracoronis with four crossed feet, Hexacoronis with six radial feet, Stylocoronis with numerous (8 or more feet). These subgenera have important relations to the corresponding genera of Zygospyrida.

Subgenus 1. Dipocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with two descending lateral feet (right and left) as prolongations of the frontal ring.

Basal ring nearly circular, with two conical, straight, parallel descending feet, which are direct lateral prolongations of the subcircular frontal ring, and half as long as it. The ovate sagittal ring bears at the apex a short conical vertical horn. All rings nearly smooth.

Basal ring elliptical, with two descending, slightly curved conical feet, lateral prolongations of the subcircular frontal ring. The ovate sagittal ring bears at the apex a cylindrical vertical horn, which is connected by two descending lateral arches (or galear arches) with the uppermost part of the frontal ring.

Subgenus 2. Tripocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with three descending feet (one caudal and two pectoral).

Basal ring violin-shaped, with three straight divergent thorny feet, about as long as the ovate sagittal ring. The dorsal part of the latter is straight, vertical, and prolonged downwards into the caudal foot, upwards into a stout, thorny, vertical apical horn. The ventral part is semicircular and gives off the lateral branches, forming the kidney-shaped sagittal ring. All the rings and their apophyses are armed with stout thorns. This and the following tripodal species may be directly derived from Cortina.

Basal ring kidney-shaped, with three large divergent curved feet, nearly twice as long as the semicircular sagittal ring. The straight dorsal part of the latter is prolonged downwards into the caudal foot, upwards into a large branched apical horn, curved backwards. Differs from the preceding species mainly in the longer curved apophyses and in the larger violin-shaped frontal ring.

Subgenus 3. Tetracoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with four descending feet (two sagittal and two lateral).

Basal ring kidney-shaped, with four stout and straight divergent feet, about as long as the sagittal ring; two of them are lateral and arise from the basal corners of the violin-shaped frontal ring (at its junction with the basal ring); two are sagittal, and arise from the basal corners of the semicircular sagittal ring (one posterior caudal and one anterior sternal). The straight dorsal part of the sagittal ring is prolonged upwards into an apical horn. All the rings are thorny.

Subgenus 4. Hexacoronis, Haeckel

Definition.—Basal ring with six radial descending feet (two sagittal, two pectoral, and two tergal feet).

Basal ring violin-shaped, with six conical, vertically descending feet, half as long as the sagittal ring; two of them are sagittal (arising from the two basal corners of the sagittal ring, caudal and sternal feet); the other four are lateral, and prolongations of the forked basal parts of the frontal ring, which is inserted on the basal ring with two forked branches; the anterior correspond to the pectoral, the posterior to the tergal feet of Hexaspyris. All the rings are thorny.

Subgenus 5. Stylocoronis, Haeckel.

Definition.—Basal ring with numerous (eight to twelve or more) descending feet.

Basal ring violin-shaped, with ten to twelve flat lamellar, vertically descending feet, about as long as the ovate sagittal ring. Frontal ring twice as broad as long, elliptical. All rings nearly smooth. Similar to a Petalospyris without lattice-work.

Basal ring elliptical, with fifteen to eighteen conical, curved, descending feet, half as long as the ovate sagittal ring. Frontal ring kidney-shaped, one and a half times as broad as long. All the rings armed with short conical spines.

Subfamily 4. Trissocyclida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large gates (four superior lateral and four inferior basal). Skeleton composed of three complete rings, perpendicular to one another; two of which are vertical (the primary or sagittal and the secondary or frontal ring), the third is horizontal (the tertiary or basal ring).

Genus 421. Tristephanium,^[40] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with eight large, simple gates of different sizes; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three simple complete rings, perpendicular to one another.

The genus Tristephanium, and the three following genera derived from it, represent together the interesting subfamily of Trissocyclida (Prodromus, 1881, p. 446). These differ from all other Coronida in the possession of three complete rings, perpendicular to one another. The first of these is the vertical sagittal ring, the second the vertical frontal ring, and the third the horizontal basal ring. Since these three rings lie in the three dimensive planes, they are perpendicular to one another; and between them remain eight large open gates. Originally the four upper or lateral gates (corresponding to those of Zygostephanus) are much larger, the four lower or basal gates (corresponding to those of Semantrum) much smaller; but afterwards the latter may reach the size of the former, so that the basal ring becomes equatorial (in Trissocircus and Trissocyclus). The common ancestral form of the Trissocyclida (Tristephanium) may be derived directly either from Semantrum (by complete development of the frontal ring) or from Eucoronis (by complete development of four basal gates).

Subgenus 1. Triostephus, Haeckel, 1881, Prodromus, p. 445.

Sagittal ring ovate, with a large thorny apical horn, smaller than the two other rings. Frontal ring violin-shaped, with a deep sagittal constriction. Basal ring also violin-shaped, in the sagittal axis constricted. Its four gates (two jugular and two cardinal) of nearly equal size. All three rings angular, armed with scattered, stout, thorny spines, which are larger in the basal half.

Sagittal ring ovate, nearly smooth, smaller than the two other rings. Frontal ring kidney-shaped, with a deep basal constriction. Basal ring violin-shaped. The jugular gates about half as large as the cardinal gates. Rods of the rings cylindrical, with few scattered thorns.

Acanthodesmia hertwigii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 539, Taf. xxxii. figs. 9a-9c.

Sagittal ring ovate or nearly semicircular; its dorsal rod straight, smooth (fig. 9c, a), its ventral rod (b) curved, thorny. Frontal ring much larger, thorny, violin-shaped, with a slight sagittal {984}constriction. Basal ring smaller than the sagittal ring, thorny, kidney-shaped, with four different gates; the two cardinal pores much larger than the two jugular pores. (The four basal pores are often much larger than in the specimen figured by Bütschli. Also the number, form, and size of the spines is very variable.)

Subgenus 2. Tristephaniscus, Haeckel, 1881, Prodromus, p. 445.

Sagittal and frontal ring of equal size and form, larger than the circular basal ring. From the four corners, in which the latter crosses the two former, arise four strong, divergent spines, branched like a deer's antler. Some smaller spines are scattered on the rings, and a bunch of four spines arises on the apical pole. The four upper gates are triangular, the four lower nearly semicircular, the latter of equal size, half as large as the former.

Genus 422. Tricyclidium,^[41] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large, partly fenestrated gates; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three latticed complete rings, perpendicular to one another.

The genus Tricyclidium differs from the preceding Tristephanium, its ancestral form, in the development of loose rudimentary lattice-work along the rings, and therefore bears to it the same relation that Plectocoronis does to Eucoronis. It may pass directly over into Dictyospyris.

Sagittal ring ovate, twice as thick as the two other larger rings, which become very thin, thread-like at the lateral junction, and are both slightly violin-shaped, in the middle sagittal plane constricted; the frontal ring larger than the basal. All three rings bear small scattered spines, which are irregularly branched, and by anastomoses of the thread-like branches form small irregular meshes along the rings. The four basal gates are of equal size.

Sagittal ring ovate, smaller than the violin-shaped frontal ring and larger than the elliptical basal ring. All three rings of nearly equal thickness, armed with short irregular branches, which are partly connected, and forming small irregular meshes along the rings. The four basal gates are of different sizes; the two anterior (jugular) gates only half as large as the two posterior (cardinal) gates.

Genus 423. Trissocircus,^[42] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large simple gates of equal size. Skeleton composed of three simple complete rings, perpendicular to one another.

The genus Trissocircus, and the following nearly allied Trissocyclus, differ from the two preceding ancestral genera in the remarkable growth of the four basal gates, which reach the size of the lateral gates. Therefore both hemispheres of the shell (the upper or apical and the lower or basal) here become equal and the basal ring becomes equatorial. Sometimes even all three rings attain the same size, so that it is difficult or impossible to distinguish them. In this curious case the Coronida exhibit a striking resemblance to some Sphæroidea.

Subgenus 1. Tricircarium, Haeckel.

Definition.—Sagittal ring smaller than the two other rings, which are both elliptical.

All three rings elliptical, of different sizes, smooth, without spines. The sagittal ring is the smallest, but two to three times as thick as the other two rings, which have the larger (transverse) axis common. The smaller (sagittal) axis of the sagittal ring is also the smaller axis of the equatorial ring, whilst the larger (principal) axis of the former is the smaller axis of the frontal ring.

Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, slightly constricted on the poles of the principal and transverse axes. The axis of the circular sagittal {986}ring is the shorter axis of the frontal and equatorial ring, and about half as long as their longer axis. All three rings smooth, without spines.

Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, distinctly constricted at the poles of the principal and transverse axes. The axis of the circular sagittal ring is the shorter axis of the frontal and equatorial ring, about one-third shorter than their longer axis. All three rings armed with short, irregularly branched spines.

Subgenus 2. Tricirconium, Haeckel.

All three rings equal, circular, smooth, their rods cylindrical (in the transverse section circular). From each pole of the three equal axes arises a short conical spine; these six spines correspond to the six corners of a regular octahedron.

All three rings equal, circular, thorny; their rods prismatic (in the transverse section triangular), with three sharp dentated edges and scattered branched thorns. From each pole of the three equal axes (which correspond to the three axes of a regular octahedron) arises a bunch of larger spines.

Genus 424. Trissocyclus,^[43] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large, partly fenestrated gates of equal size. Skeleton composed of three complete latticed rings, perpendicular to one another.

The genus Trissocyclus differs from its nearly allied ancestral form Trissocircus only in the development of small anastomosing branches along the edges of the rings. The incomplete lattice-work, produced by these anastomoses, partly protects the eight large gates. The three rings are either of equal or of different sizes.

Subgenus 1. Tricyclarium, Haeckel.

Definition.—Sagittal ring circular, smaller than the other two rings, which are both elliptical.

Sagittal ring circular, smaller than the other two equal elliptical rings. On each of the six corners (or crossing points of every two rings) are developed four small pores, forming a cross around the poles of the three axes. All three rings smooth, without spines.

Sagittal ring circular, smaller than the two other equal elliptical rings. From the edges of all three rings are developed small branches, which by irregular ramification and anastomoses form small irregular meshes along the rings. Similar to Trissocircus octostoma, but with thicker rings; it may be developed from the latter species by connection of the branches which border the rings.

Subgenus 2. Tricyclonium, Haeckel.

All three rings equal, circular, thorny; their rods prismatic, three-sided, with three denticulate edges; the teeth of the lateral edges become branched, and form by anastomoses of the branches small irregular meshes, which partly protect the eight large open gates.

Family LI. Tympanida, Haeckel.

Parastephida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Stephoidea with two parallel horizontal rings, an upper mitral and a lower basal ring; both connected by complete or incomplete vertical rings, or by parallel vertical columellæ.

The family Tympanida (or Parastephida) differs from the other Stephoidea in the development of two horizontal rings, which lie in horizontal planes and arise from the upper and the lower poles of the primary sagittal ring. Therefore the same formation, which we found in the Semantida on the basal pole only of the main axis, here takes place also on its apical pole. On both poles arise at each side from the sagittal ring two corresponding pairs of curved branches: the lateral ends of the opposite branches (dorsal and ventral branch) become united in the frontal plane and so form two complete horizontal rings. The upper ring, composed of the superior or mitral branches, may be called the mitral ring, the lower ring, formed by the inferior or basal branches, the basal ring. Both rings are commonly of nearly equal size, more rarely of different sizes. Their connection is effected either by the primary (sagittal) ring only, or also by secondary vertical rings, a frontal ring in the lateral plane, or some diagonal meridian rings between the latter and the former. These vertical rings, which connect both horizontal rings in the form of "columellæ," may be either complete or incomplete; in the latter case their apical and basal parts are lost, the dorsal and ventral parts only being preserved.

The Tympanida develop a great variety of different forms, greater than in the three other families of Stephoidea, so that we may distinguish here not less than sixteen genera and seventy-two species. Hitherto only three species were known: Prismatium tripleurum, figured in 1862 in my Monograph, Tympanidium barbadense, figured by Bury in the "fossil Polycystins of Barbados," and Tympaniscus fibula, described in 1875 by Ehrenberg as a Ceratospyris fibula. The number of species in this large and richly developed group will be considerably augmented by further researches. A great many of them exhibit remarkable relations to different Nassellaria. For better survey of the whole family we distinguish here four subfamilies, the first of which (Protympanida) is probably the common ancestral group of the other three. They may have been derived originally either from the Semantida or directly from the Stephanida.

The first subfamily, Protympanida, exhibits a complete primary or vertical sagittal ring, bearing on the upper part a horizontal mitral ring, on the lower part a horizontal basal ring. Therefore the gates of these two parallel rings become bisected by the sagittal ring, each divided into a right and a left half. The sagittal ring itself becomes divided by the two horizontal rings into four parts or rods; two opposite of these are more or less vertical; the dorsal (posterior) and the ventral (anterior) rod; the two other rods are more or less horizontal; the mitral (upper) and the basal (lower) rod.

In Protympanium (Pl. 93, fig. 14), the simplest and most primitive form of Tympanida, the connection of the two horizontal rings is effected only by the dorsal and ventral rods of the sagittal ring forming two parallel more or less vertical "columellæ." In all other Protympanida accessory columellæ are developed between the latter. In the greater number we find two secondary columellæ in the lateral plane, being the lateral {989}segments of an incomplete frontal ring (Acrocubus, Pl. 93, figs. 15-17). Between the latter and the former there are sometimes developed four tertiary columellæ, as segments of two crossed incomplete diagonal rings (Tympanidium, Pl. 94, figs. 1, 18). At other times we find six columellæ; here probably the frontal ring is cleft into halves on each side (Tympaniscus, Pl. 94, figs. 4-7). Some genera are distinguished by the development of an equatorial ring, or a third horizontal ring (between the upper mitral and the lower basal ring); this equatorial ring is either complete (Microcubus Pl. 94, figs. 8-10) or incomplete, developed only laterally (Octotympanum, Pl. 94, figs. 2, 3). The genus Toxarium (Pl. 93, figs. 18-20) is distinguished by the development of accessory pairs of bows in the frontal plane, upper or galear bows and lower or thoracal bows, remarkable as beginnings of the accessory joints, which we distinguish in many Spyroidea and Cyrtoidea as "galea and thorax."

The second subfamily of Tympanida are the Paratympanida, in which the two horizontal rings become closed by lattice-work. The numerous columellæ connecting the two rings are here either divergent (Paratympanum, with two unequal rings, Pl. 94, fig. 14) or parallel and vertical (Lithotympanum, with two equal rings, Pl. 83, fig. 1). The shell of the latter assumes the form of a drum.

A third small subfamily, Dystympanida, is represented by a single genus only, Dystympanium (Pl. 94, figs. 15, 16). Here only the upper or mitral ring is closed by lattice-work, whilst the lower or basal ring exhibits quite a simple opening, a large "basal gate" which has probably arisen by loss of the basilar rod of the sagittal ring. These curious forms exhibit a remarkable resemblance to some Monocyrtida, and also to the Dictyocha (Phæodaria).

The fourth subfamily, the Eutympanida, are distinguished by the simple wide aperture of the two horizontal rings; the upper enclosing a simple "mitral gate," the lower a simple "basal gate." Here probably the two horizontal parts of the sagittal ring (the upper mitral rod and the lower basilar rod) are lost by reduction; its two vertical parts (the dorsal and ventral rods) only remaining and forming the two parallel columellæ, which connect the two horizontal rings (Parastephanus, Pl. 93, fig. 21). In this group also secondary columellæ are commonly developed between the two rings, alternating with the two primary columellæ. Pseudocubus (Pl. 94, figs. 11, 12), resembling an obelisk, exhibits four divergent columellæ; the two sagittal of these are probably the vertical parts of the primary ring, whilst the two lateral are the halves of an incomplete frontal ring. In Lithocubus (Pl. 82, fig. 12) the four columellæ are parallel and vertical, the two rings being equal; the shell here assumes the form of a geometrical cube. Prismatium is distinguished by three parallel columellæ; two of these are probably parts of a frontal ring, whilst the third is the remains of a reduced sagittal ring. In Circotympanum (Pl. 94, fig. 17) and in Lithotympanum (Pl. 82, fig. 11) the number of the columellæ is augmented, there being six to eight or more; in the former they are divergent {990}(the two rings being of different sizes), in the latter parallel (the two rings being equal); the fundamental form of the former is a truncated pyramid, of the latter a prism.

Comparing these differences between the four subfamilies of Tympanida, we may suppose that the common ancestral group are the Protympanida, derived from the Semantida by the formation of a mitral ring. If the two horizontal rings become closed by lattice-work, the Paratympanida arise. When the mitral ring only becomes latticed, the basal ring being simple, the Dystympanida originate. Finally, the fourth subfamily, the Eutympanida, may be derived from the Protympanida by the loss of the two horizontal parts of the sagittal ring.

The two horizontal rings (upper mitral and lower basal) and the two vertical rings (primary sagittal and secondary frontal), which thus compose the loose framework of the Tympanida, are rarely smooth, commonly armed with spines or branches, similar to those of the Coronida. The rods or bars are either roundish (with circular transverse section) or angular (commonly with triangular transverse section). The paired branches of the two vertical rings often preserve the characteristic arrangement inherited from the Semantida and Stephanida. The two horizontal rings sometimes exhibit typical apophyses, which recur in the Spyroidea and Cyrtoidea. The mitral ring may possess one odd apical horn and two paired frontal horns (Pl. 93, figs. 16, 17, 19, 23). The basal ring sometimes bears the three typical feet of Cortina (Pl. 93, figs. 16, 22), one odd caudal foot and two paired pectoral feet. Sometimes a fourth (sternal) foot is developed (Pl. 94, fig. 4), at other times only two lateral feet (Pl. 94, figs. 5, 6).

Synopsis of the Genera of Tympanida.

Subfamily 1. Protympanida, Haeckel.

Definition.—Tympanida with two bisected horizontal rings, connected by the complete vertical sagittal ring. (The upper mitral ring and the lower basal ring become divided by the complete primary or sagittal ring into two horizontal symmetrical gates, two mitral gates on the apical and two basal gates on the basal pole.)

Genus 425. Protympanium,^[44] Haeckel, 1881, Prodromus, p. 447 (sensu emend.).

Definition.—Tympanida with two bisected horizontal rings, connected by two vertical columellæ.

The genus Protympanium, is the most simple form of all Tympanida, and probably the common ancestral form of this family. It arises from Lithocircus by the development of two horizontal rings, perpendicular to the primary sagittal ring. The upper or mitral ring arises by lateral union of two pairs of superior branches, the lower or basal ring by union of two pairs of basal branches of the primary vertical ring.

Mitral and apical ring of equal size, elliptical, smooth, somewhat smaller than the connecting thorny sagittal ring.

Dimensions.—Diameter of the two horizontal rings 0.12, of the sagittal ring 0.15.

Mitral and apical rings of equal size, thin, elliptical, smooth, larger than the broad connecting sagittal ring. The latter bears on the apical and on the basal pole two divergent straight spines (lying in the frontal plane), the two apical (or horns) somewhat smaller and not so spiny as the two basal spines (or feet). In the frontal plane there arise from the two horizontal rings on each side two small opposite spines (remnants or beginnings of the lateral frontal ring?).

Dimensions.—Diameter of the two horizontal rings 0.11, of the sagittal ring 0.07.

Mitral ring smaller than the basal ring; both rings circular, rough. Sagittal ring in size between the two former. All three rings covered with very small thorns.

Dimensions.—Diameter of the mitral ring 0.08, of the sagittal ring 0.1, of the basal ring 0.12.

Genus 426. Acrocubus,^[45] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ. No equatorial ring.

The genus Acrocubus is the most primitive of those remarkable Tympanida, the skeleton of which represents more or less exactly the form of a geometrical cube. A simple complete sagittal ring bears on the superior and on the inferior part two opposite pairs of lateral branches; by union of the convergent branches of each side there arise two horizontal parallel quadrangular rings, which are bisected by the sagittal ring. Therefore the superior ring encloses two triangular mitral gates, the inferior two triangular basal gates. The lateral corners of the two gates of each side are connected by a vertical rod or columella. These two parallel columellæ are the remaining middle parts of the secondary or frontal ring, which is incomplete on the superior and on the inferior face of the body. If the sagittal ring also become incomplete, by the loss of the superior and inferior part (the anterior and posterior only remaining), then Acrocubus is transformed into Lithocubus.

Subgenus 1. Apocubus, Haeckel.

Mitral ring somewhat smaller than the basal ring; both rings rhombic, with curved outlines. Sagittal ring elliptical, with six pairs of nodulate protuberances. Four columellæ curved. Nodal points without radial spines.

Mitral ring of the same size as the basal ring; both rings square, smooth, with straight outlines. Sagittal ring also square, smooth. Four columellæ straight. Nodal points without radial spines. The shell has the form of a regular geometrical cube, the edges of which are represented by the rings.

Subgenus 2. Dipocubus, Haeckel.

Mitral ring smaller than the basal, both rings square, with thick straight rods. Sagittal ring tuberculate, square, equatorial part thinner. Four columellæ curved, the two lateral ones prolonged downwards into two vertical parallel straight feet of half their length.

Mitral and basal rings of nearly equal size, square, with thick curved rods. Sagittal ring elliptical, in the equatorial part thinner. Frontal ring tuberculate. Four columellæ curved, the two lateral ones prolonged downwards into two vertical, tuberculate feet of half their length.

Mitral and basal rings, as well as the sagittal ring, of the same form as in the preceding nearly allied species. The two lateral columellæ are prolonged not only downwards into two short {994}vertical feet, but also upwards into two curved bows, which are united in a vertical ascending horn, arising from the apical pole of the sagittal ring.

Subgenus 3. Tripocubus, Haeckel.

Definition.—Basal ring with three descending feet (one odd caudal and two paired lateral).

Mitral ring smaller than the basal, both rings square, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital simple horn, downwards into a caudal foot. Two lateral columellæ prolonged downwards into two pectoral feet. All three feet conical, about as long as the height of the cube.

Mitral ring smaller than the basal, both rings elliptical, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital horn, downwards into a caudal foot, as in the preceding species. As in the latter, also, the two lateral columellæ are prolonged downwards into two pectoral feet, but also upwards into two convergent horns, which are united with the occipital horn (commencing the formation of a galea). Rings and feet somewhat thorny.

Subgenus 4. Tetracubus, Haeckel.

Definition.—Basal ring with four descending feet (two sagittal and two lateral).

Mitral and basal rings of the same size, square, with straight rods, sagittal ring also square. The four vertical columellæ are nearly parallel and straight, prolonged upwards into four short conical horns, downwards into four longer conical feet. (The shell has nearly the form of a geometrical cube, the eight corners of which are prolonged into eight vertical conical spines, four smaller ascending and four larger descending.)

Mitral ring smaller than the basal, both rings elliptical, with curved rods. Four columellæ thorny, also curved, divergent downwards, prolonged upwards into four thorny convergent horns, downwards into four larger branched divergent feet. The two sagittal horns and feet (anterior and posterior) are smaller than the two lateral (right and left); therefore the fundamental form of this species is distinctly amphithect (as in the Ctenophora).

Genus 427. Toxarium,^[46] n. gen.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ. In the frontal plane two galear bows project upwards, and two thoracal bows downwards.

The genus Toxarium differs from its ancestral form Acrocubus in the development of two pairs of peculiar bows, placed in the lateral or frontal plane; the upper pair projects above the mitral gates, and may be called the "galear bows," the lower pair projects below the basal gates of the cubical shell, and may be called the "thoracal bows." Both pairs are produced originally by the development of two forked vertical spines, arising in the frontal plane on both poles of the principal axis from the sagittal ring (compare Protympanium amphipodium, Pl. 93, fig. 14). The apical fork-branches become connected with the lateral corners of the mitral gates, the basal branches with those of the basal gates. By development of lattice-work between the bows and the rings some Spyroidea (Amphispyris, &c.) may have arisen. The important genus Toxarium may be divided into three subgenera. In Toxellium all the bows are simple, in Toxonium, all are forked; in Toxidium, the galear bows are simple, the thoracal bows forked.

Subgenus 1. Toxellium, Haeckel.

Galear and thoracal bows simple, of about the same size as the frontal bows between them; all bows armed with scattered simple conical spines. Sagittal constriction deep, half as long as the whole shell. Lateral outlines of the shell nearly parallel.

Galear and thoracal bows simple, armed with scattered simple spines of about equal size, smaller than the smooth frontal bows between them. Sagittal constriction very flat. Therefore the frontal perimeter of the shell is nearly circular.

Galear bows simple, smaller than the frontal bows, and these again smaller than the simple thoracal bows; therefore the shell increases in breadth towards the base, and resembles the skeleton of the thorax of one of the higher vertebrates (the bow-pairs corresponding to rib-pairs, the ventral part of the sagittal ring to the sternum, the dorsal part to the vertebral column). Sagittal constriction very deep. All bows are armed with scattered, irregularly branched spines.

Galear and thoracal bows simple, of nearly equal size, larger than the frontal bows between them. Therefore the shell is constricted in the equatorial plane. Sagittal constriction also deep. All bows armed with scattered, irregularly branched spines.

Subgenus 2. Toxidium, Haeckel.

Galear bows simple, thoracal bows forked, both somewhat smaller than frontal bows; all bows armed with scattered simple conical spines, mostly developed at the thoracal bows. Both galear bows are united in a central vertical columella, which arises from the apex of the sagittal ring, and is prolonged into an apical horn. Therefore the sagittal constriction exists only in the basal half of the inversely cordate shell.

Galear bows simple, thoracal bows forked, both somewhat broader than the frontal bows. Shell therefore slightly constricted in the equatorial plane. Sagittal constriction rather deep, equal in the apical and basal parts. All bows armed with scattered spines, which are partly simple, partly forked.

Galear bows simple, smaller than the frontal bows, which are again smaller than the thoracal bows. Therefore the breadth of the shell increases towards the base. Sagittal constriction flat in the apical part, deep in the basal part. All bows armed with small irregularly scattered spines; at the base six larger divergent feet (two lateral, two anterior, and two posterior).

Subgenus 3. Toxonium, Haeckel.

Galear and thoracal bows forked, smaller than the frontal bows, all bows thorny, without larger spines. Sagittal constriction on both poles deep. Lateral outlines of the shell nearly parallel.

Galear and thoracal bows forked, the former smaller than the frontal bows, the latter larger. Sagittal constriction rather flat on the apical pole, which bears a vertical forked horn, very deep on the basal pole of the primary ring. All bows armed with numerous spines, which are partly simple, partly forked, and mainly developed at the basal part of the thoracal bows.

Genus 428. Microcubus,^[47] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ, which are bisected again by an equatorial ring.

The genus Microcubus is derived from its ancestral form Acrocubus by development of a third horizontal ring, which lies in the equatorial plane, parallel to the upper mitral and the lower basal ring. Whilst these latter are both bisected by the complete vertical sagittal ring, the equatorial ring is complete, and connected at the poles of the sagittal axis with the principal ring, and at the poles of the transverse axis with the frontal ring. Therefore the shell exhibits not eight large gates as in Acrocubus, but twelve, viz., four horizontal gates (two superior mitral and two inferior basal), four upper vertical gates (between the mitral and the equatorial ring), and four lower vertical gates (between the basal and the equatorial ring).

All twelve gates simple, irregularly ovate or pentagonal. Frontal ring on the sides concave, constricted by the equatorial ring. All rings curved, armed with short irregular thorns. No larger basal spines.

All twelve gates simple. Frontal ring on the sides convex, not constricted by the equatorial ring. All rings tuberculate, with irregular roundish knots. No larger basal spines. Similar to the preceding species; but the five rings are much thicker and tuberculate (not thorny); the twelve gates are therefore relatively smaller.

All twelve gates simple, ovate. Frontal ring on the sides convex, not constricted by the equatorial ring, nearly twice as broad as long. All rings thorny, very thin, except only the broad angular sagittal ring. No larger basal spines.

All twelve gates simple, square. Frontal ring square, not constricted by the equatorial ring. All rings smooth, quadrangular. Basal ring with four short vertical conical feet, two of which (right and left) are inferior prolongations of the frontal ring, and arise from the lateral corners of the {999}basal gates; two others are prolongations of the sagittal ring (sternal and caudal), and arise from the medial corners of the basal gates. (The shell is like a small cube with four feet.)

Eight gates (two mitral, two basal, and four superior) simple; four inferior gates fenestrated by arachnoidal irregular threads. Frontal ring square, constricted on the sides by the equatorial ring. Basal ring with four short conical vertical feet, as in the preceding species. Sagittal ring with a vertical horn on the apex. All rings with small scattered thorns.

Four gates (two mitral and two basal) simple; eight lateral gates (four superior and four inferior) fenestrated by arachnoidal irregular threads. Frontal ring convex, not constricted by the equatorial ring. Basal ring with six short conical divergent feet (two sagittal and four lateral). Sagittal ring with an apical horn. (Resembles some Spyroidea.)

Genus 429. Octotympanum,^[48] n. gen.

Definition.—Tympanida with two bisected horizontal rings converging laterally and connected in the lateral poles of the equatorial plane. Eight large gates.

The genus Octotympanum differs from all other Tympanida in the peculiar connection of the two horizontal rings, which here reach the maximum of their growth, converge towards the equator, and come into direct contact on the poles of the equatorial transverse axis. Therefore the shell appears to be composed of three complete vertical meridian rings, the middle of which (the sagittal ring) is free and simple; the two other (subfrontal) rings are grown together at the lateral poles of the equatorial plane; commonly at these poles there arises (on the right and left) a strong lateral spine, and the base of this (or the crossing point of the two touching horizontal rings) corresponds to the remnants of the shortened frontal ring. The crown-shaped shell exhibits therefore eight large gates; two superior (mitral) and two inferior basal gates, two larger anterior (facial) and two larger posterior (occipital) gates. Seen from the lateral poles {1000}only two of the former are visible, and represent the figure of a vertical 8; seen from the sagittal poles, only two of the latter are visible, in the form of a larger horizontal eight

. Octotympanum may be derived from Acrocubus by reduction of the lateral frontal ring to a knot (or cross-point), and by maximal extension of the two parallel horizontal rings, which become curved downwards laterally and touch at the lateral poles.

Mitral gates smaller than the basal gates; upper halves of the two lateral meridional rings smaller than the lower halves. Rings with few scattered thorns; four larger simple spines, nearly horizontal in the equatorial plane; two on the poles of the sagittal axis, two on the poles of the lateral axis. Four other large spines, nearly vertical at the four lowermost basal points of the subfrontal rings.

Mitral gates of the same size as the basal gates; upper and lower halves of the meridional rings of equal size. Rings armed with numerous stout, thorny, simple and forked spines; four very large branched spines in the equatorial plane, nearly horizontal, two on the poles of the sagittal, two on the poles of the transverse axis, the latter curved downwards.

Mitral gates smaller than the basal gates, the lower halves of the lateral rings being broader than the upper halves. Rings very spiny, armed with numerous branched spines; ten very large arborescent spines on the lateral rings; two on the poles of the transverse axis, eight on the prominent corners of the diagonal axes (four upper and four lower); sagittal ring thorny.

Mitral and basal gates of equal size, the lower and upper halves of the two crossed lateral rings being nearly equal. Rings armed with numerous branched spines; two very large spines, similar to the antlers of a deer, on the poles of the lateral axis; their branches about half as large as the whole shell. Sagittal ring nearly smooth, with few small thorns on the poles of the main axis.

Genus 430. Tympaniscus,^[49] n. gen.

Definition.—Tympanida with two bisected horizontal rings, which are connected by three vertical meridional rings (or six columellæ).

The genus Tympaniscus and the following Tympanidium differ from all preceding Tympanida in the multiplication of the vertical columellæ, which connect the two horizontal bisected rings. Tympaniscus exhibits six columellæ, which may be regarded as halves of three meridional rings. Only one, however, of these is complete (the sagittal ring, which bisects the mitral and the basal ring); the two other meridional rings (placed in diagonal planes) may be regarded as produced by lateral bifurcation of an incomplete frontal ring; this appears to be already foreshadowed in the preceding Octotympanum.

Basal ring larger than the mitral ring, with numerous irregular short spines but without descending feet. Six columellæ strongly curved, in the lower half thicker and thorny; the four lateral much thinner than the two sagittal. Apex of the jointed sagittal ring with a conical horn.

Basal ring of about the same size as the mitral ring, with two lateral descending feet, which are parallel and vertical, simple, without spur, half as long as the sagittal ring. The latter is ovate, twice as long and broad as the two circular frontal rings.

Basal ring smaller than the mitral ring, with two lateral descending feet, which are nearly parallel and vertical, obtuse, about as long as the sagittal ring, and which bear on the outside a horizontal spur. Sagittal ring hexagonal, very stout, with a caudal appendix at the base, and with a small sagittal arch, bearing a stout spinulate double knob at the apex. The two subfrontal rings depressed, twice as broad as high, on the outside thorny, connected at each side in the lower half by a double transverse arch.

Basal ring of about the same size as the mitral ring, with three large and stout divergent feet (two lateral and one caudal). Sagittal ring stout, broader than the two spiny subsagittal rings; the upper part of the latter bears two ascending arches, which are united with the large apical horn arising from the apex of the sagittal ring. Six columellæ nearly vertical, slightly curved on the outside; their lateral edges armed with numerous simple or forked spines.

Basal ring larger than the mitral ring, with four short vertical three-sided pyramidal feet of equal size (two lateral and two sagittal); the feet are three-sided pyramidal, with finely denticulate median edges, and bear at the base a horizontal thorny spur. Sagittal ring at the apex with a very large cross-shaped horn, bearing two horizontal thorny lateral branches; the horn is supported by an anterior and a posterior arch. Six columellæ strongly curved and dentate.

Ceratospyris fibula, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 3.

Basal ring of about the same size as the mitral ring, with six large conical descending feet; these are prolongations of the six columellæ, nearly of the same length, slightly divergent, and bear at the base a strong horizontal spur. The six columellæ are strongly curved, spiny, and bear above small arches, which are united with the apical horn of the sagittal ring.

Basal ring of the same size as the mitral ring, with six very large and six alternating smaller, slightly divergent, curved feet, about as long an the shell; the larger are the basal prolongations of the six curved, thorny columellæ. Mitral ring spiny, not overgrown with arches, as in the similar preceding species.

Genus 431. Tympanidium,^[50] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, which are connected by four vertical meridional rings (or eight columellæ).

The genus Tympanidium differs from all other Protympanida in the development of four vertical rings, placed in four different meridional planes. Only one of these is complete, the primary sagittal ring; the three others are incomplete, inserted on the two horizontal rings, which are formed by the paired mitral and basal branches of the sagittal ring; one of these three lies in the frontal plane, the two others in diagonal meridional planes (between the frontal and sagittal). The shell therefore exhibits twelve large gates, four of which are horizontal (the two superior mitral and the two inferior basal gates); the eight others are vertical, separated by the eight columellæ, or the halves of the four meridional rings. In the subgenus Tympanomma the number of gates amounts to sixteen, the four lateral gates being bisected by an incomplete equatorial ring. The genus Tympanidium may be derived from Acrocubus by development of the two diagonal rings (between the frontal and sagittal).

Subgenus 1. Tympanura, Haeckel.

Shell with twelve gates; the four lateral gates simple. Basal gates of the shell larger than the mitral gates. Sagittal ring ovate, much smaller than the three other meridional rings, which are armed with numerous large elegant spines, bearing a lanceolate leaf on a thin pedicle. The sagittal ring bears a bunch of similar spines only at the apex, and on both poles of the sagittal axis (in the equator) a single forked spine, with two thorny branches.

Shell with twelve gates; the four lateral gates simple. Basal and mitral gates of about equal size. Shell similar to that of the preceding species, differing mainly in the different armature; the numerous spines, covering the convex outside of the four vertical rings, are not leaf-shaped, but conical, short, of very variable size, partly simple, partly irregularly branched.

Subgenus 2. Tympanomma, Haeckel.

Definition.—Shell with sixteen gates (eight median gates, paired on both sides of the sagittal ring, and eight lateral gates, paired on both sides of the frontal ring). The four lateral gates of the two preceding species (subgenus Tympanura) are bisected in Tympanomma by the lateral parts of an incomplete equatorial ring.

Shell with sixteen gates; the four lateral gates double, bisected by the lateral parts of an incomplete equatorial ring. Basal gates nearly rectangular, of the same breadth as the pentagonal mitral gates, but twice as long. Equatorial outline of the shell (seen in fig. 18 from the apical pole) octagonal. All rods of the shell thin, smooth.

"Hollow cylinder," &c., Bury, 1862, Polycystins of Barbados, pl. xvi. fig. 1.

Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal gates kidney-shaped, of the same breadth as the circular mitral gates, but twice as long. Equatorial outline of the shell elliptical. All rods of the shell thin, smooth.

Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal and mitral gates of the shell of about equal size, roundish. Equatorial outline of the shell violin-shaped, with a sagittal constriction. All rods of the shell armed with short irregular spines.

Subfamily 2. Paratympanida, Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two fenestrated horizontal rings, which are connected by a variable number of vertical rods or columellæ. The shell therefore becomes more completely latticed than in the other Tympanida, and approaches that of the Spyroidea.

Genus 432. Paratympanum,^[51] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two latticed horizontal rings, connected by numerous descending and diverging columellæ; mitral ring smaller than the basal ring.

The genus Paratympanum and the following nearly allied Lithotympanum form together the small subfamily of Paratympanida, distinguished from the other Tympanida by the fenestration of the two parallel horizontal rings. These rings in Lithotympanum are both equal, whilst in Paratympanum, the basal ring is larger than the mitral ring; therefore the connecting rods or columellæ are in the former parallel and vertical, in the latter divergent and descending. Two opposite ones of these columellæ are parts of the primary sagittal ring, two others are parts of the lateral or frontal ring, whilst the remainder are afterwards intercalated. Paratympanum may be derived from Dystympanium by fenestration of the basal ring.

Six divergent columellæ, about as long as the diameter of the hexagonal mitral ring, connect it with the larger hexagonal basal ring. Lattice of the mitral ring hemispherical, with six roundish pores, surrounding a central apical horn. Lattice of the basal ring with one large central pore, surrounded by numerous peripheral pores. Rings and rods smooth, without spines.

Dimensions.—Length of the shell 0.07; breadth of the mitral ring 0.06, of the basal ring 0.09.

Eight divergent columellæ, about as long as the diameter of the octagonal mitral ring, connect it with the larger circular basal ring, and bear at each end a divergent, strong, conical spine. Lattice-plate of both rings slightly convex, with numerous subregular circular pores, smooth, without surface spines.

Ten divergent columellæ, only half as long as the diameter of the decagonal mitral ring, connect it with the larger circular basal ring. Lattice-plate of the mitral ring nearly hemispherical of the basal ring flat, both with numerous irregular roundish pores and scattered spines. Margin of both rings spiny.

Genus 433. Lithotympanum,^[52] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two latticed horizontal rings, connected by numerous parallel and vertical columellæ; mitral and basal rings of equal size.

The genus Lithotympanum has the form of a cylindrical drum, the two fundamental faces of which (the mitral and basal gates) are closed by lattice-work. Both horizontal rings are equal, whilst in the preceding Paratympanum the basal gate is larger than the mitral. It may be derived from the latter by equalisation of these two rings, or directly from Dystympanium by fenestration of the basal ring.

Both lattice-plates slightly convex; the mitral plate with six larger marginal pores and one central pore separated by numerous smaller pores; the basal plate with seven large pores only (one central and six peripheral). Surface and margin of the plates uneven, with roundish prominent dimpled tubercles. Both rings connected by ten to twelve simple cylindrical vertical columellæ.

Both lattice-plates flat, with numerous irregular roundish pores of variable size. Surface thorny. Margin with numerous irregular spines, directed upwards on the mitral, downwards on the basal plate. Both rings connected by eight simple cylindrical vertical columellæ.

Subfamily 3. Dystympanida, Haeckel.

Definition.—Tympanida with fenestrated mitral ring and simple open basal ring; both horizontal rings connected by numerous vertical or divergent columellæ.

Genus 434. Dystympanium,^[53] n. gen.

Definition.—Tympanida with two horizontal rings, connected by numerous (six to eight or more) divergent columellæ. The upper mitral ring is smaller and latticed, the lower basal ring larger and open.

The genus Dystympanium, representing a peculiar subfamily, differs from all other Tympanida in the different shape of the two parallel horizontal rings. The upper or mitral ring is closed by a lattice-plate (as in Paratympanum), the lower or basal ring is simple and open (as in Eutympanium). Dystympanium may therefore be regarded as an intermediate form between these two genera, and may perhaps be derived from Paratympanum by loss of the lower lattice-plate.

Basal ring circular, with eighteen to twenty short conical divergent spines. Mitral ring about two-thirds as broad, hexagonal, with six ascending spines on the six corners. The latter are connected with the former by six simple, straight, obliquely descending columellæ, about as long as the diameter of the mitral ring. Mitral lattice-plate slightly convex, with seven roundish pores (six peripheral pores around a central pore).

Dimensions.—Diameter of the basal ring 0.09, mitral ring 0.06; length of the columellæ 0.05.

Basal ring hexagonal, with six larger spines at the six corners, and numerous smaller ones between them. Mitral ring half as broad as the basal ring, also with six angular spines. The latter are connected with the former by six divergent curved columellæ, about as long as the diameter of the basal ring. Mitral lattice-plate flat, with irregular roundish pores.

Dimensions.—Diameter of the basal ring 0.1, mitral ring 0.05; length of the columellæ 0.09.

Basal ring circular, with eight larger and numerous smaller divergent spines. Mitral ring two-thirds as broad as the basal ring, octagonal, with eight conical ascending spines on the eight corners. The latter are connected with the former by eight divergent, curved columellæ, as long as the diameter of the mitral ring. Mitral lattice-plate nearly hemispherical, with nine circular pores (eight peripheral pores around one central pore).

Dimensions.—Diameter of the basal ring 0.12, mitral ring 0.08; length of the columellæ 0.09.

Subfamily 4. Eutympanida, Haeckel.

Definition.—Tympanida with two simple horizontal rings, which are connected by a variable number of vertical rods or columellæ. Therefore the shell exhibits a large simple mitral gate on the upper, and a large simple basal gate on the lower side; between the two a variable number of lateral gates.

Genus 435. Parastephanus, Haeckel, 1881, Prodromus, p. 446.

Definition.—Tympanida with two simple horizontal rings, connected by two vertical columellæ.

The genus Parastephanus is the simplest among the Eutympanida, and exhibits only two vertical rods or columellæ, which connect the two parallel horizontal rings. One of these latter must be regarded as the mitral or superior ring, the other as the basal or inferior ring; whilst the two parallel columellæ, connecting both, are the remaining vertical parts of the sagittal ring, the upper and lower parts of which are lost. By loss of the latter Parastephanus has probably been derived from Protympanium.

Two horizontal rings smooth, circular, of equal size, connected by two curved smooth columellæ, which are somewhat shorter than the diameter of the rings.

Two horizontal rings smooth, elliptical or nearly circular, of equal size, connected by two vertical, slightly curved columellæ, which are about as long as the radius of the rings. Each ring bears two simple lateral spines, which in the mitral ring are curved downwards, in the basal ring upwards, possibly the last remains of a reduced frontal ring.

Two horizontal rings thorny, of equal size, irregularly ovate or nearly semicircular, and of somewhat asymmetrical form. The two connecting parallel columellæ are straight, cylindrical, about as long as the diameter of the rings. The peculiar asymmetry in the form of the rings raises the possibility that the two columellæ in this species are the remaining parts of a frontal ring, and that the sagittal ring has altogether disappeared. In this case the convex half of both rings would be the ventral, the straight half the dorsal part.

Two horizontal rings elliptical, thorny, of different sizes, the basal ring one and a half times as broad as the mitral ring. The two connecting columellæ are curved, somewhat longer than the diameter of the mitral ring.

Dimensions.—Diameter of the basal ring 0.09, mitral 0.06; length of the columellæ 0.07.

Genus 436. Prismatium,^[54] Haeckel, 1862, Monogr. d. Radiol., p. 270.

Definition.—Tympanida with two simple horizontal rings, connected by three vertical columellæ.

The genus Prismatium was hitherto the only known form of the Tympanida, and the only species described in 1862 in my Monograph was Prismatium tripleurum (loc. cit., p. 270, pl. iv. fig. 6). A new species from the Challenger collection (Pl. 93, fig. 22), Prismatium tripodium, explains the true structure of this remarkable genus. The skeleton is composed of nine siliceous rods, corresponding to the edges of a trilateral prism. Six of these are horizontal, and enclose the two parallel triangular horizontal gates, the superior of which is formed by the mitral or coryphal, and the inferior by the basal or cortinar ring. The three other rods are vertical and nearly parallel, and connect (as lateral edges of the prism) the corresponding corners of the two parallel horizontal triangles. Two of these vertical columellæ, together with the two horizontal parallel rods connecting them, represent the complete frontal ring, whilst the third vertical columella is the posterior half of the sagittal ring, the other parts of which are lost.

Mitral ring triangular, somewhat smaller than the triangular basal ring, both connected at the corners by three vertical, slightly curved columellæ. From the six corners arise six radial spines of different size and form; the two paired spines of the mitral ring are simple and very small, whilst those of the basal ring are three times as long and bear a lateral branch. The odd spine of the third corner is on both rings larger, and distinguished by some thorns. This difference seems to indicate that these two odd spines correspond to the apical horn and the caudal foot of Cortina, and the columella between them is the rest of the reduced sagittal ring. In this case the quadrangular vertical ring, which is composed of the two paired columellæ and the two connecting horizontal rods, would be probably the frontal ring.

Prismatium tripleurum, Haeckel, 1862, Monogr. d. Radiol., p. 270, Taf. iv. fig. 6.

Acanthodesmia prismatium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 799.

Mitral and basal rings of equal size, equilateral triangular, both connected at the corners by three vertical equal columellæ. From the six corners arise six short, equal, conical radial spines. The nine rods of the shell correspond to the nine edges of a triangular equilateral prism.

Genus 437. Pseudocubus,^[55] n. gen.

Definition.—Tympanida with two simple horizontal rings of different sizes, connected by four divergent columellæ.

The genus Pseudocubus exhibits the characteristic form of an obelisk, or a truncated four-sided pyramid. The four edges of this obelisk, or the four "columellæ," are the remaining parts of the two incomplete vertical rings; two opposite edges are the dorsal and ventral rod of the sagittal ring; the two alternate edges between these are the lateral rods of the frontal ring. The two horizontal rings, which become connected by the four divergent columellæ, are the smaller mitral ring and the larger basal ring; both are either square or nearly circular.

Mitral ring square, with circular gate and two divergent simple spines on each corner. Basal ring twice as broad, square, with four convex sides and one simple spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Mitral ring square, with one stout pyramidal spine on each corner. Basal ring twice as broad, square, also with a single strong spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Mitral ring circular, two-thirds as broad as the subcircular, or nearly square, basal ring; both rings with a simple spine on the two sagittal corners (dorsal and ventral), with a forked or branched larger spine on the two lateral corners (right and left). All twelve rods more or less curved and thorny.

Genus 438. Lithocubus,^[56] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two simple horizontal rings of equal size, connected by four parallel vertical columellæ.

The genus Lithocubus is very remarkable for the regular cubical form of the skeleton, which is composed of twelve siliceous rods, corresponding to the twelve edges of a cube. Eight of these are horizontal, and enclose the two parallel square horizontal gates, the superior mitral and the inferior basal gate. The four other rods are vertical, parallel, and connect (as lateral edges of the cube) the corresponding corners of the two horizontal squares. Two opposite ones of these four vertical columellæ are the remaining halves of the incomplete sagittal ring; the two alternate are the remaining halves of the incomplete frontal ring. The four lateral gates between these four columellæ are also square or rectangular, and either of the same size as the two horizontal gates, or somewhat larger. Lithocubus may be derived from Acrocubus by reduction of the coryphal and the basal part of the primary sagittal ring, the only remaining parts of which are the anterior and the posterior columellæ.

The twelve rods, corresponding to the edges of the geometrical cube, are straight and smooth; the eight corners provided with a small conical thorn. The shell exhibits six equal square sides, and represents therefore exactly the geometrical form of a cube.

The twelve rods of the cubical shell are slightly curved, convex, smooth, as in the similar preceding species. It differs from that in the development of eight slender radial spines, arising from the eight corners of the geometrical cube, from two to three times as long as its diameter, and lying opposite in pairs in its diagonals.

Acanthodesmia vinculata, J. Müller, 1856 (partim), Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. i. fig. 7 (not 4-6).

The twelve rods of the cubical shell are curved and armed with scattered, simple, short spines. The figure 7 of Johannes Müller (loc. cit.) corresponds exactly to the Mediterranean form observed by me at Portofino, and is quite different from his true Acanthodesmia vinculata (loc. cit., figs. 4-6), so that I have no doubt he did observe these two different species (compare above, p. 975).

The twelve rods of the cubical shell are stout and slightly curved, armed with numerous, simple, and irregularly branched spines. Eight larger spines, branched like a deer's antler, arise from the eight corners of the cube.

Dimensions.—Diameter of the cube 0.1 to 0.12; length of the corner spines 0.05 to 0.08.

Genus 439. Circotympanum,^[57] n. gen.

Definition.—Tympanida with two simple different horizontal rings, connected by numerous (six to eight or more) divergent columellæ.

The genus Circotympanum comprises those Tympanida in which two simple horizontal rings of different size (an upper smaller "mitral ring," and a lower larger "basal ring") are connected by a variable number of divergent rods or columellæ (at least six or eight). Circotympanum is probably derived from Tympaniscus or Tympanidium by partial reduction of the sagittal ring, the upper (apical) and lower (basal) part of which is lost. The geometrical fundamental form is a truncated pyramid with six to eight or more edges.

Mitral and basal ring hexagonal, the latter twice as broad as the former, each with a simple small spine on the six corners. Six columellæ nearly straight, as long as the radius of the basal ring. All rods with three prominent edges.

Mitral and basal rings octagonal, the latter one and a half times as broad as the former. Eight columellæ slightly curved, thorny. The mitral ring bears on each corner a short ascending spine, the basal ring a larger, thorny, obliquely descending spine, which has some recurved thorns on the upper edge. All rods more or less thorny.

Mitral and basal rings circular, the latter nearly twice as broad as the former, both armed with scattered irregular thorns. Ten columellæ smooth, curved.

Genus 440. Eutympanium,^[58] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two simple equal horizontal rings, connected by numerous (six to eight or more) parallel and vertical columellæ.

The genus Eutympanium contains those Tympanida in which the drum-shaped shell is composed of two simple, parallel and equal horizontal rings, and numerous vertical and parallel rods or columellæ connecting them. The number of the latter is at least six or eight. Two opposite of these must be regarded as remaining vertical parts of the sagittal ring, two others as parts of the frontal ring, whilst the other columellæ (between the former and the latter) are secondary and intercalated. Therefore Eutympanium may be derived from Tympanidium by reduction and loss of the apical and basal parts of the sagittal ring.

Eight parallel and vertical columellæ, simple, straight and smooth. Both horizontal rings equal, circular, each armed with eight to twelve short conical thorns.

Eight vertical columellæ slightly curved, thorny. Both horizontal rings equal, octagonal, each armed with eight large, irregularly-branched spines, which on the mitral ring are directed obliquely upwards, on the basal ring downwards.

Eight thorny columellæ, obliquely descending and curved like a bow, divergent in the upper part, convergent in the lower. Basal ring circular, mitral ring octagonal. Both horizontal rings armed with eight stout thorny spines, which on the mitral ring are smaller and directed obliquely upwards, on the basal ring larger and directed downwards, each with a recurved hook.

Ten parallel and vertical columellæ straight and smooth, cylindrical. Both horizontal rings equal, circular, armed with numerous short conical spines, divergent in all directions. Ten to twenty spines on each ring larger than the others.

Twelve vertical columellæ, slightly curved, smooth. Mitral and basal rings circular, both horizontal rings armed with twelve stout, irregularly-branched spines, which are prolongations of the columellæ, and on the mitral ring directed upwards, on the basal ring downwards.

Order VI. CYRTELLARIA, Haeckel, 1881.

Definition.—Nassellaria with a complete lattice-shell enveloping the central capsule.

Suborder I. SPYROIDEA, Haeckel.

Spyridina, Ehrenberg (pro parte), 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Zygocyrtida, Haeckel, 1862, Monogr. d. Radiol., p. 291.

Zygocyrtida, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 501.

Acanthodesmida, R. Hertwig, 1879, Organismus der Radiol., p. 68.

Spyrida vel Spyroidea, Haeckel, 1881, Prodromus, p. 440.

Definition.—Nassellaria with a complete lattice-shell, exhibiting constantly a bilocular cephalis with a sagittal constriction.

The suborder Spyroidea, and the two following closely allied suborders, Botryodea and Cyrtoidea, represent together that large group of Radiolaria which I first described in my Monograph (1862, pp. 272, 280) as the family Cyrtida, but afterwards as a separate order (or sublegion) under the name Cyrtellaria (1883, Jena. Sitzungsber., Feb. 16, p. 18). This group comprises all those Monopylea or Nassellaria which possess a complete lattice-shell, whilst the preceding Plectellaria never develop a perfect fenestrated shell enveloping the central capsule. The Spyroidea differ from the other Cyrtellaria (Botryodea and Cyrtoidea) in the bilocular shape of the cephalis, which is bisected by the sagittal ring and a corresponding longitudinal constriction into two symmetrical halves.

The Spyroidea appear in the first system of Polycystina of Ehrenberg (1847, loc. cit., pp. 53, 54) as the fourth of his seven families, under the name Spyridina, with the following definition:—"Testæ nucleo destitutæ (associatæ et coalitæ); cellulæ binæ clathratæ, nucis forma amplæ, strictura longitudinali levius discretæ." Ehrenberg united them with his "Polycystina composita or Spumellaria" and separated them from the closely allied "Polycystina solitaria or Nassellaria." He distinguished among them five genera, two of which have no external appendages (Dictyospyris and Pleurospyris), whilst the other three possess spiny or lamellar appendages (Ceratospyris, Cladospyris, and Petalospyris). These five genera and the accompanying definitions were also repeated in the same terms in the last system of Ehrenberg (1875, loc. cit., p. 157). In my Monograph (1862, pp. 280, 291) the Spyroidea are enumerated as a {1016}subfamily of the Cyrtida, under the name Zygocyrtida, with the following definition:—"Lattice-shell divided by an annular sagittal longitudinal constriction into two neighbouring equal joints or chambers." I adopted at that time the above five genera of Ehrenberg, only eight species of which were known.

Richard Hertwig gave in 1879 the first accurate description of the central capsule of the Spyroidea, and demonstrated that they possess the same characteristic structure of the capsule, with a porochora and a podoconus, that is common to all Monopylea. He separated the Zygocyrtida from the other Cyrtida, and united them with the Stephoidea (Lithocircus) in the family Acanthodesmida. In my Prodromus (1881, p. 449) I adopted that division and put the "Spyrida or Spyroidea" as a separate family between the Cyrtoidea and Stephoidea. I there gave the following definition:—"Monopylaria gemina, testa silicea clathrata gemina, cameris binis juxta compositis, annulo verticali sagittali contiguis, capsula centrali a testa inclusa. Promorpha dipleura vel bilaterali, dextro et sinistro antimero symmetricis, plano sagittali annuloque separatis. Polum superiorem axis verticalis vel principalis plerumque spina apicalis (vel occipitalis) occupat, polum inferiorem ostium clathratum (poris tribus aut quatuor aut pluribus) et spina caudalis (posterior). Ad dextram et sinistram duæ spinæ laterales distant. Ab hac forma tripoda (Monocyrtida triradiata acuta cum annulo mediano) diversæ Spyridum formæ derivandæ sunt." I there divided the Spyrida into seven subfamilies and forty-eight genera. Bütschli in 1882 published accurate researches on the Zygocyrtida in his Beiträge zur Kenntniss der Radiolarien-Skelete, insbesondere der der Cyrtida (Zeitschr. f. wiss. Zool., vol. xxxvi. p. 501, Taf. xxxii.). He gave a very exact anatomical description of the skeleton of several fossil Spyroidea of Barbados, and pointed out their close affinity to the Acanthodesmida on the one hand, and to the Cyrtida on the other. Regarding their phylogenetical relation, he supposed that the Zygocyrtida have descended from the Acanthodesmida (our Stephoidea) and are the ancestors of all other Cyrtida. The best part of this valuable paper of Bütschli is his exact description of the sagittal ring and its apophyses, producing the basal plate; and the general conception thus derived of the essential parts of the skeleton in all Monopylea, bearing a sagittal ring. But his general conclusions were partly erroneous, since the fossil Spyroidea and Cyrtoidea of Barbados, upon which they were founded, contain only the minority of genera of the large group; and many important and typical forms remained unknown to him.

The numerous new genera discovered in the rich collection of the Challenger, and mainly in the wonderful Radiolarian ooze of the Central Pacific (Stations 263 to 274) throw a new light upon the complicated affinities of the whole group, and manifest a far greater richness in developmental variations and admirable morphological productions than Bütschli could suppose. The following description, however, must remain very incomplete, since the exact and thorough study of all individual forms, in the same manner as {1017}Bütschli had done in the case of a small number of species, would require several years. I can therefore only give the basis of further researches.

In the majority of Spyroidea the three essential elements of the Nassellarian skeleton are easily recognisable, viz.:—A, the vertical sagittal ring of the Stephoidea; B, the basal tripod of the Plectoidea, and C, the latticed cephalis of the Cyrtellaria. These three elements are constantly so combined that the primary sagittal ring bisects the cavity of the lattice-shell and produces an external, longitudinal, more or less distinct constriction, separating the lateral inflated halves of the bilocular cephalis; while the three divergent feet of the basal tripod descend from the cortinar or basal plate of the cephalis. The number of the feet is often augmented; they are rarely wanting (probably reduced). The sagittal ring is constantly present, though its relation to the shell-wall exhibits many modifications. The bilocular form of the fenestrated cephalis, with its sagittal constriction, is characteristic of all true Spyroidea, and separates them from the Botryodea (with multilobate cephalis) on the one hand, and from the Cyrtoidea (with simple cephalis) on the other. There are, however, some intermediate forms between these three suborders of Cyrtellaria, which show a direct transition to one another. Almost constantly the length of the three dimensive axes in the cephalis of the Spyroidea is so different that the lateral or frontal axis is the longest, the sagittal or dorso-ventral axis the shortest, and the principal or longitudinal axis intermediate between them. As in all dipleuric or bilaterally symmetrical forms, the two poles of the frontal axis are equal, whilst the two poles of the sagittal and of the principal axis are more or less different. In only a few forms of Spyroidea these differences are difficult to make out; usually the dorsal side is distinctly different from the ventral, and the apical side from the basal. A perfect knowledge of the dipleuric shell requires therefore accurate observation from all six sides.

The suborder of Spyroidea is here divided into four different families. In the first and original family, the Zygospyrida, the shell is represented by the bilocular cephalis only. The second family, Tholospyrida, is distinguished by a fenestrated cupola or galea, a hemispherical or conical dome, arising from the upper or coryphal face of the cephalis. In the third family, Phormospyrida, a thorax is developed, or a fenestrated basal chamber, arising from the lower or basal face of the cephalis. The fourth family, Androspyrida, combines the characters of the second and the third family, a galea arising from the upper and a thorax from the lower face of the cephalis.

The bilocular cephalis, as the most important and constant part of the skeleton in all Spyroidea, requires a further general consideration. Its lattice-work, very variable in the numerous species, is usually more or less different on the six sides of the nut-shaped shell. Its most important part is the horizontal basal plate or lower face, and the sagittal ring arising from it in the vertical median plane. This part of the shell corresponds exactly to the skeleton of the Semantida, and exhibits the same modifications {1018}as in that family; it is therefore probable that the majority of the Spyroidea (if not the whole group) have been derived directly from the Semantida by further development of network from the fenestrated ring of Clathrocircus. Whilst in this latter Semantid the two lateral sides of the central capsule remain naked, in the Spyroidea they become enclosed and covered by lattice-work, which arises on the right and left from the ring. In some forms, however, as in the Ceratospyris acuminata of Hertwig, and in my Perispyrida, the frontal ring also of the Coronida and the mitral ring of the Tympanida appear as the initial parts of a complete latticed cephalis.

The basal plate of the cephalis, or the "cortinar plate," the "Basal-Scheibe" of Bütschli, has constantly, according to this author, two pairs of pores, an anterior smaller pair of jugular pores (the pores I of Bütschli) and a posterior larger pair of cardinal pores (the pores II in his description) (compare Pl. 95, figs. 3, 6). This applies to the majority of Spyroidea, but by no means to the whole group. We find basal plates with two pores only (Pl. 95, fig. 1), with three pores (figs. 2, 5), with six pores (figs. 4, 7), with nine pores (Pl. 87, fig. 2), &c. The forms with two basal pores may be derived directly from Semantis (Pl. 92, figs. 1, 2); the common forms with four pores from Semantrum (figs. 3-5); the rarer forms with six pores from Semantidium (figs. 6, 7); and the forms with three pores from Cortiniscus, &c. In this as well as in other respects the variety of different forms and of developmental variations is far greater than Bütschli (1882, loc. cit.) supposed. The bars between the pores of the basal plate possess the same value and the same names as in the Semantida (compare above, p. 954).

The coryphal plate of the cephalis, its upper or apical lattice-plate, does not exhibit such important differences as the opposite basal plate, is far less variable, and is usually pierced by numerous, smaller pores. Some larger pores lie, often in pairs, on the right and left side of the sagittal constriction, and have in some groups a regular form and disposition. Either in the middle of the coryphal plate, or (usually) nearer to its dorsal margin, there arises in majority of Spyroidea an apical horn, directed either vertically or more or less obliquely backwards. In many Spyroidea three horns are developed in the coryphal plate, the odd middle apical horn and two paired frontal or lateral horns arising on each side of the latter and directed more forwards (Pl. 84, figs. 9-12). Sometimes the apical horn disappears, while the two frontal horns remain (Pl. 95, fig. 12).

The anterior or ventral plate of the cephalis (the "Hinterseite" of Bütschli), and the posterior or dorsal side (the "Vorderseite" of that author), exhibit in the majority of Spyroidea more or less marked differences in the number, form, and disposition of their pores, which require a far more accurate description than is here possible. Usually the sagittal constriction of these two plates, produced by the primary vertical ring, is deeper and sharper in the middle of the ventral than in that of the dorsal plate. On both sides of the ring there appear in each plate usually two or three pairs of larger pores, whilst numerous smaller pores are situated towards the lateral sides. We may {1019}distinguish the large pores of the ventral plate as facial pores (upper orbital, middle nasal, and lower maxillary pores), and the opposite large pores of the dorsal plate as occipital pores (upper epoccipital, middle mesoccipital, and lower suboccipital pores). A closer comparison of these pores, and of the separating bars in the numerous Spyroidea, may show a regularity of development similar to that offered by the homologies of the parts in the skeleton of the Echinodermata, or of the bones in the skull of the Vertebrata.

The two convex lateral plates of the cephalis, or the right and left sides, both symmetrically equal, do not exhibit the same regularity in the shape, number, and disposition of the pores that the four other sides do. Usually their pores are much smaller and more numerous. In very few forms only a distinct frontal ring is visible (corresponding to that of the Coronida), and in this case the lateral pores are sometimes disposed symmetrically on both sides of this ring. These Spyroidea may have arisen directly from corresponding forms of Coronida.

The sagittal ring (or the primary vertical ring) inherited from the Stephanida and Semantida, shows in the Spyroidea great variety in its form and in its relation to the cephalis. These variations are far greater than Bütschli (1882, loc. cit.) supposed. We may distinguish the following six principal cases:—A. The ring lies completely in the wall of the cephalis, and causes a deep sagittal constriction in it. In this case the lower part or basal segment of the ring separates the basal pores into pairs; its anterior part or ventral rod the facial pores; its upper part or coryphal rod the apical pores; and its posterior part or dorsal rod the occipital pores. No part of the ring is free in the shell-cavity. B. The greater part of the ring lies enclosed in the shell-wall; only its dorsal rod arises free in the shell-cavity and ascends vertically or obliquely to the apex, where it is usually prolonged into the apical horn. This seems to be the most common case. C. The coryphal and the basal part of the ring lie enclosed in the shell-wall, with its dorsal and ventral rod free in the shell-cavity; the dorsal rod ascends vertically to the apex, the ventral rod obliquely upwards to the upper part of the facial plate (the nasal or orbital region). This case, regarded by Bütschli as the usual one, is far less common than he supposed. D. The greater part of the ring lies free in the shell-cavity, its basal rod only is enclosed in the shell-wall, and separates the right from the left group of the cortinar pores. This case seems to be rarer than the preceding. E. The whole ring lies free in the shell-cavity, and is connected with the sagittal constriction of the shell-wall by numerous short radial beams. The distance of the shell-wall from the enclosed ring is usually least on the basal rod, and greatest on the dorsal rod. F. The whole ring lies free in the shell-cavity (as in the preceding case), and is connected by numerous short radial beams with a secondary larger, concentric sagittal ring, which is developed in the longitudinal constriction of the shell-wall.

Comparing these six principal cases, in respect of the relation of the primary sagittal ring to the cephalis of the Spyroidea, we may suppose that they represent together a continuous phylogenetical series of which the first (A) is the original, and the last (F) the latest case; and that the true cause of the various changes is a successive separation of the ring, which becomes more and more free and independent from the lattice-plate of the cephalis. Since the intimate study of the structure of the cephalis in many Spyroidea is very difficult, it requires further accurate observations (from all six sides of the shell). There are also some other more difficult complications of its structure, which cannot be solved without exact study and extended comparison.

Of peculiar importance for the differentiation of the numerous genera of the Spyroidea are the basal feet or the descending and diverging apophyses, which are developed from the base of their cephalis. In general they exhibit the same typical shape which we find in the Plectellaria as well as in the Cyrtoidea, and which we regard therefore as an important common character of the majority of Nassellaria. We may therefore distinguish here also the three primary, and the other ones as secondary feet. The three primary feet, or the "cortinar feet," are the same that we found in the Plagonida and Plectanida, in Cortina and Cortiniscus among the Stephoidea, and in the majority of Cyrtoidea. They also reappear in the same characteristic disposition and connection with the basal plate of the cephalis, in the majority of Spyroidea. The odd caudal foot (c) is the lower prolongation of the dorsal rod of the sagittal ring, which is prolonged upwards into the apical horn. The two paired pectoral feet, however (p′, p′′), are the descending prolongations of the coracal rods (e) which separate the jugular pores (i) from the cardinal pores (k) of the cortinar plate (compare Pl. 95, figs. 2-6).

The three cortinar feet are nearly equally developed in the majority of Spyroidea (compare Pls. 84, 89). But often the odd caudal foot exhibits a different shape from that of the two paired pectoral feet, and in many genera of the group it becomes more or less rudimentary. It has quite disappeared in the subfamily Dipospyrida (Pl. 85); here the two pectoral feet only are developed (often excessively), and are usually opposite in the frontal plane. Such dipodal forms, very common in the Spyroidea, are never found in the Cyrtoidea.

The secondary feet, which we contrast with the three primary feet as later productions, exhibit great variations in number and development. Very frequently three interradial secondary feet become developed, alternating with the three primary cortinar or perradial feet, and opposed to them in pairs (Pl. 95, figs. 7, 8). In these hexapodal Spyroidea (or Hexaspyrida) an odd anterior or sternal foot (z) is opposite to the odd caudal foot, and two paired posterior or tergal feet (t′, t′′) to the two pectoral feet. When the sternal foot becomes rudimentary or lost, pentapodal forms arise (Pentaspyrida, Pl. 95, figs. 9-11), and when the two odd feet (caudal and sternal) disappear, tetrapodal forms arise with two pairs of feet (Therospyrida, Pl. 89, figs. 5, 6). The latter differ from {1021}those quadrupedal forms in which two opposite sagittal feet (the caudal and sternal) alternate in the form of a cross with two paired lateral or pectoral feet (Tetraspyrida, Pl. 53, figs. 19, 20). In many Spyroidea the number of basal feet is greatly increased, and they form a regular radial corona around the basal plate, like a circle of tentacles (Polyspyrida, Pl. 87). In this latter case the feet are usually flat and lamellar, whilst in the other groups they exhibit a very variable form, as is seen in Pls. 83-89.

The Central Capsule of the Spyroidea has been accurately observed in only a few genera, and requires a further exact examination regarding the different modifications which occur in their different families. It is very probable that these will agree with the well known modifications in the corresponding groups of Cyrtoidea. The characteristic Monopylean structure of the capsule (with porochora and podoconus) was first described by Richard Hertwig in his Ceratospyris acuminata (loc. cit., p. 72, taf. vii. fig. 2). I found the same afterwards in many other forms. In the Zygospyrida and Tholospyrida the central capsule seems to be usually bilobate (bisected by the sagittal ring), and enclosed in the two chambers of the cephalis. The two lobes of the capsule (right and left) are equal and connected by a smaller middle part, which contains the transverse elliptical nucleus and is enclosed by the sagittal ring; often each lobe contains a large oil-globule. In some forms, however, three or four lobes (sometimes perhaps more) are developed, which pierce the cortinar pores of the basal plate and depend freely between the basal feet (Pl. 53, fig. 19). In the Phormospyrida and Androspyrida the formation of such basal lobes seems to be more frequent; they are here enclosed by the thorax. Usually each lobe contains a large oil-globule. In Nephrospyris (Pl. 90) and in some similar genera the central capsule is violin-shaped, deeply bisected by the sagittal ring; in each of the two lobes a series of oil-vesicles is developed at both poles of the transverse axis (figs. 7, 10); the nucleus, a transverse cylindrical body, is placed in the latter. In the periphery of the voluminous calymma of this singular genus a large number of globular cells are developed (figs. 7, 10), probably symbiotic xanthellæ. In some forms of Nephrospyris these xanthellæ are enclosed by a peculiar inflated girdle, developed in the periphery of the kidney-shaped skeleton (Pl. 90, figs. 1, 4-6).

Synopsis of the Families of Spyroidea.

Family LII. Zygospyrida, n. fam. (Pls. 84-87).

Definition.—Spyroidea without galea and thorax; the shell consisting of the bilocular cephalis only and its apophyses.

The family Zygospyrida is by far the richest among the four families of Spyroidea, the number of genera in the whole suborder amounting to forty-five, in the former to twenty-eight; and the number of species in the latter to two hundred and thirty-seven, in the former to one hundred and seventy-two. The number of individuals also found in many species of Zygospyrida is far greater than in any species of the three other families. The shell of the Zygospyrida is represented by the bilocular cephalis only, and never develops a galea (as in the Tholospyrida) nor a thorax (as in the Phormospyrida and Androspyrida). The three latter families have therefore been derived from the former as their common ancestral group.

The Zygospyrida are very similar and nearly related to the Monocyrtida, and in both groups the cephalis alone represents the whole shell. Therefore in 1882, Bütschli, in the paper mentioned above (p. 1016), maintained the opinion, that these two groups were identical. But there is this important difference between them, that in the Zygospyrida (as in all Spyroidea) the cephalis is bilocular, with a sagittal constriction, separating the right and left chambers. In the Monocyrtida, however (as in all Cyrtoidea), the cephalis is unilocular, forming a quite simple chamber without sagittal constriction. Correspondingly the primary sagittal ring in all Zygospyrida is well preserved and usually complete, while in the Monocyrtida it is never complete, and often quite absent. Another difference is indicated by the form of the central capsule, which in the Zygospyrida is usually bilobed, and more developed in the frontal axis, whilst in the Monocyrtida it is commonly ovate, and more developed in the principal axis.

The important questions of the origin and phylogenetical relation of these two similar groups of Nassellaria form a very complicated and difficult problem, and we do not at present possess the means of solving it. It may be that a part of the Monocyrtida has been derived from the Zygospyrida (as Bütschli erroneously supposes for all), but the contrary is also possible. A third possibility is the independent origin of both groups from the Semantida. But we shall see afterwards, in the description of the Monocyrtida, that a great part of this group may with greater probability be derived from the Plectoidea than from the Stephoidea, and that another part of them has probably been derived quite independently from the Nassellida. Regarding the complicated relations of these similar groups, mentioned above (pp. 892-894), it seems hopeless here to discuss further their difficult affinities; but in any case it seems useful or even necessary to separate the Monocyrtida from the Zygospyrida.

The cephalis of the Zygospyrida possesses all the characteristic features which we have described above as belonging to the Spyroidea in general (p. 1017), and a survey of the Pls. 84-87 exhibits the most important modifications of its shape (compare also Pl. 95, figs. 1-13). Therefore we may avoid useless repetitions by referring to the description given above. We will only point out that the bilocular character of the cephalis (in opposition to the simple cephalis of the Monocyrtida) in the majority of Zygospyrida is apparent on the first view, and that it is always demonstrated by an accurate examination of the sagittal ring and its relation to the longitudinal constriction of the cephalis (compare p. 1019). The basal plate or cortinar plate exhibits usually four typical pores (two smaller jugular, i, and two larger cardinal, k), but this is by no means a general rule, as Bütschli thought; moreover, instead of four cortinar pores, there are frequently found three or six or some other numbers (compare above, p. 1018).

The top of the cephalis in the majority of Zygospyrida bears an apical horn, as an upper prolongation of the dorsal rod of the sagittal ring; it is often of unusual size and shape (Pl. 85, figs. 5-11; Pl. 95, fig. 8, &c.). In several genera two lateral or frontal horns are developed on both sides of the former (Pl. 84, figs. 9-12; Pl. 86, figs. 5-13). Sometimes these two alone are present, while the original apical horn is lost by reduction (Pl. 95, fig. 12). In other genera the apical face bears no horns; probably they are lost by reduction.

The greatest variety of forms is produced in the Zygospyrida by the different number, disposition, and shape of the feet, or the basal apophyses arising from the base of the cephalis. Regarding these remarkable differences, we may distinguish eight subfamilies. The common ancestral group of all are probably the Tripospyrida, which possess the three typical basal feet of Cortina and Cortiniscus, an odd caudal and two paired pectoral feet (Pl. 84). From these may be derived the Dipospyrida (Pl. 85) by loss of the caudal foot, the Tetraspyrida by development of an odd sternal foot (Pl. 53, figs. 7, 8, 19), and the Hexaspyrida by development of three secondary interradial between the three primary perradial feet. The Pentaspyrida may have been derived from the latter by loss of the sternal foot (Pl. 95, figs. 9-11), and the Therospyrida by loss of the two sagittal feet (Pl. 89, figs. 5, 6). The Polyspyrida bear numerous (seven to twelve or more, often twenty to thirty) basal feet, forming a corona around the cortinar plate (Pl. 87); they may have been derived from the Tripospyrida or Hexaspyrida by further multiplication of the feet. Finally, the Circospyrida exhibit no feet at all (Pl. 89, figs. 7-12); they may be derived either from one of the preceding groups by complete reduction and loss of the basal apophyses, or directly from those Semantida which have no feet (Semantis, Semantrum, Clathrocircus, &c.).

Synopsis of the Genera of Zygospyrida.

Subfamily 1. Tripospyrida, Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida tripoda, with three descending basal feet (the same as in Cortina, an odd posterior or caudal foot and two paired anterior or pectoral feet).

Genus 441. Tripospyris,^[59] Haeckel, 1881, Prodromus, p. 441.

The genus Tripospyris (Pl. 84, figs. 1-7) is in the large group of Spyroidea probably the most original and typical form, from which, as a common ancestral form, all other genera of this polymorphous suborder may be derived. The shell is usually shaped like a nut or thorax, and exhibits two paired lateral chambers, which are separated by a distinct sagittal ring and a slighter or deeper sagittal constriction. The dorsal rod of the ring is prolonged at the upper pole into an ascending apical horn, at the lower pole into a descending caudal foot, whilst two paired pectoral or lateral feet arise from the anterior pole of the basal rod. These three divergent basal feet and the apical horn are the same four typical radial spines which we have encountered already in Plagoniscus (Plagonida), in Plectaniscus (Plectanida), in Cortina (Stephanida), and in Cortiniscus (Semantida). Compare above, p. 891. From all these Plectellaria, Tripospyris differs in the development of a complete bilocular lattice-shell, having the characters of the true Spyroidea. The numerous species of this genus may be placed in different subgenera, according to the different number of collar pores or cortinar pores in the basal plate (two, three, four, six, or more). These differences are very important, however difficult to make out; the following system therefore is a provisional one, and requires further accurate observations.

Subgenus 1. Tripospyrantha, Haeckel.

Definition.—Basal plate with two large pores only (the primary jugular pores of Semantis).

Shell ovate, smooth, about as long as broad, with slight ovate sagittal stricture, and broad primary ring in its wall. Basal plate with two large kidney-shaped collar pores only (cardinal pores). Facial and occipital plates each with two pairs of large annular pores, and ten to twelve pairs of small lateral pores. Apical horn and the three basal feet of equal length, one and a half times as long as the shell, three-sided prismatic, straight, divergent.

Shell ovate, smooth, one and a third times as long as broad, with sharp ovate sagittal stricture and broad primary ring. Basal plate with two large cardinal pores only. Occipital plate with two pairs of very large pores; facial plate and lateral sides with numerous smaller irregular roundish pores. Apical horn small, conical, curved, half as long as the three basal feet, which are club-shaped and three-edged, with thinner bases and half as long as the shell, strongly divergent.

Shell subspherical, smooth, somewhat broader than long, with slight sagittal stricture and subcircular parietal primary ring. Basal plate with two large semicircular cardinal pores. Facial and occipital plate each with two pairs of large annular pores and an odd large subapical pore; lateral sides with very numerous small roundish pores. Apical horn and caudal foot club-shaped, half as long as the shell, angular, simple; the two pectoral feet somewhat longer, nearly vertical, and at the distal end with a small incision, nearly forked.

Shell thorax-shaped, smooth, twice as broad as long, with deep sagittal stricture, two vaulted ovate bosoms and smaller ovate internal primary ring. Basal plate with two large ovate cardinal pores. Facial plate with three pairs, occipital plate with four pairs of large annular pores; the other lattice-work loose, with small and numerous irregular polygonal pores. Apical horn and caudal feet slender and thin, curved, shorter than half the shell; two pectoral feet also small, widely divergent, more or less curved, deeply forked.

Subgenus 2. Tripospyrella, Haeckel.

Definition.—Basal plate with three large collar pores (two paired posterior cardinal pores, and an odd anterior sternal pore).

Ceratospyris triomma, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxi. fig. 3.

Shell subspherical, tuberculate, with slight sagittal stricture and circular internal ring. Basal plate with three large pores, which are sometimes (but not in every specimen) surrounded by a {1027}circle of very small pores. The other lattice-work with numerous small roundish pores. Apical horn small, oblique, about as long as the shell. Three feet very large, cylindrical, curved, widely divergent, four to five times as long as the shell. (In Ehrenberg's description the caudal foot is erroneously described as "frontal spine"; its figure exhibits the basal plate.)

Dimensions.—Shell 0.07 to 0.09 diameter; horn 0.06 long, feet 0.3 to 0.4 long.

Shell nearly hemispherical, papillate, with slight sagittal stricture and semicircular internal ring. Basal plate with three large pores (sometimes, as in the figured specimen, with some small accessory peripheral pores). The other lattice-work with subregular circular pores. Apical horn shorter than the three basal feet, but of similar form, like an elegant ovate dimpled cone, spinulate, with a smooth spindle-shaped pedicle, about as long as the shell.

Shell thorax-shaped, spiny, with deep sagittal stricture and semicircular internal ring. Basal plate with three large collar pores. Facial plate with four pairs, occipital plate with three pairs of large annular pores; the other pores small, subregular, circular. Apical horn and the feet slender, three-sided pyramidal, about as long as the shell.

Subgenus 3. Tripospyrissa, Haeckel.

Definition.—Basal plate with two pairs of collar pores (two larger posterior cardinal pores and two smaller anterior jugular pores).

Shell thorax-shaped, thorny, with deep sagittal stricture and subcircular ring. Basal plate with four large collar pores (two smaller ovate jugular, and two larger pentagonal cardinal pores). Facial and occipital plates also each with two pairs of large annular pores; lateral sides with smaller irregular polygonal pores. Apical horn and the three feet slender, prismatic, divergent, longer than the shell.

Shell subspherical, spiny, with slight sagittal stricture and ovate internal ring. Basal plate with four large collar pores. Facial plate with three pairs and occipital plate with two pairs of large roundish annular pores; lateral lattice with smaller irregular pores. Apical horn and the three feet subcylindrical, about half as long as the shell, straight, divergent, with a spherical, spinulate knob at the distal end.

Ceratospyris clavata, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 539, Taf. xxxii. fig. 13, a-c.

Shell subspherical, compressed, rough, with slight sagittal stricture and ovate internal primary ring. Basal plate with four large collar pores (fig. 13a, loc. cit.). The other lattice-work with irregular small roundish pores. Apical horn and the three feet short and thick, scarcely half as long as the shell, with a roundish spinulate knob at the distal end.

Dimensions.—Length of the shell 0.07 long, 0.08 broad; horn and feet 0.02 to 0.03 long.

Shell nearly cubical, spiny, with deep sagittal stricture and subcircular ring. Basal plate with four large collar pores. Facial and occipital plates each also with two pairs of large square annular pores; lateral pores irregular polygonal. Apical horn half as long as the feet, which are three times the length of the shell, cylindrical, slightly curved.

Subgenus 4. Tripospyromma, Haeckel.

Definition.—Basal plate with six or more collar pores. Commonly two small anterior jugular pores, two large middle cardinal pores, and two small posterior cervical pores; sometimes several small accessory collar pores.

Shell thorax-shaped, tuberculate, with deep sagittal stricture and semicircular internal primary ring. Basal plate with three pairs of pores. Facial plate with two pairs, occipital plate with four pairs of large annular pores. Lateral pores smaller, irregular, polygonal. Apical horn and caudal foot half as long as the shell and as the two pectoral feet; all four spines cylindrical, two to three times as long as the shell, slightly curved.

Shell nut-shaped, thorny, with sharp sagittal stricture and subcircular ring. Basal plate with three pairs of large pores. Facial and occipital plates each with three pairs of large squarish pores. Lateral pores small and numerous, irregular roundish. Apical horn half as long as the shell and the three feet; all four spines straight, cylindrical, with thickened club-shaped end.

Shell thorax-shaped, smooth, with two vaulted bosoms, separated by a deep sagittal stricture and an internal primary ring. Basal plate constricted, with three pairs of collar pores. The other lattice-work with subregular circular pores. Apical horn and the three feet shorter than the shell, straight, divergent; their inner half thinner, cylindrical, smooth, their outer half an ovate dimpled cone.

Cladospyris tribrachiata, Ehrenberg, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. xxi. fig. 8.

Shell subspherical, smooth, with slight sagittal stricture and numerous, very small circular pores. Basal plate with numerous small pores. Apical horn and the three divergent feet very large and stout, straight, three-sided prismatic, with dentate edges, two to three times as long as the shell.

Shell nut-shaped, smooth, with deep sagittal stricture and broad ring. Basal plate with three pairs of small pores. Facial and occipital plates each with a pair of very large holes. Apical horn and caudal foot simple conical, two pectoral feet forked or irregularly branched.

Genus 442. Triceraspyris,^[60] Haeckel, 1881, Prodromus, p. 441.

The genus Triceraspyris has arisen from the preceding ancestral Tripospyris by the development of two paired frontal horns, so that the shell here bears six appendages, {1030}three superior or coryphal spines and three inferior or basal spines; two of these are odd and dorsal (the apical horn and the caudal foot), the four others are paired and ventral (the frontal horns and the pectoral feet). The numerous species of this genus may be divided into three subgenera, according to the simple or branched shape of the ascending horns and of the descending feet.

Subgenus 1. Triospyris, Haeckel, 1881, Prodromus, p. 441.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores irregular roundish, two pairs of larger pores on each side of the ring. Basal plate with three large pores. Horns and feet slender cylindrical, straight, divergent; three horns about as long as the shell, three feet twice as long.

Shell subspherical, smooth, with slight sagittal stricture. Pores small and numerous, subregular roundish. Basal plate with two large pores (?). Apical horn conical, short, half as long as the shell and the two lateral horns, which are curved outwards. All three feet equal, cylindrical, strongly curved and divergent, twice to three times as long as the shell.

Dimensions.—Shell 0.07 long, 0.08 broad; horn 0.04 to 0.08 long, feet 0.15 to 0.2 long.

Ceratospyris didiceros, Ehrenberg, 1875, Abhandl. d. Akad. d. Wiss. Berlin, p. 66, Taf. xxi. fig. 6.

Shell nut-shaped, thorny, with superficial sagittal stricture. Pores large, irregular roundish. Basal plate with four larger pores. Apical horn and caudal foot small, conical, shorter than half the shell. The two frontal horns longer, slender conical. The two pectoral feet very large, cylindrical, nearly parallel, vertical, slightly curved, twice to three times as long as the shell.

Dimensions.—Shell 0.07 long, 0.09 broad; two sagittal spines 0.02 long, two lateral horns 0.04 long, two lateral feet 0.15 to 0.25 long.

Subgenus 2. Triospyrium, Haeckel.

Ceratospyris furcata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 8.

Shell nut-shaped, tuberculate, with slight sagittal stricture. Pores numerous, irregular roundish. Basal plate with four large pores. Three horns small, conical, shorter than half the shell. Three feet large, cylindrical, curved, about twice as long as the shell, forked at the distal end.

Dimensions.—Shell 0.07 long, 0.08 broad; horns 0.02 long, feet 0.1 to 0.12 long.

Shell nut-shaped, mammillate, with slight sagittal stricture. Pores numerous, subregular circular. Basal plate with nine pores (three larger central and three alternate pairs of smaller peripheral, as in Pl. 87, fig. 2). Three horns equal, straight, divergent, shorter than the shell, in the basal half cylindrical, in the distal half spindle-shaped. Three feet cylindrical, twice as long as the shell, nearly parallel, vertical, at the distal end divergent, with a recurved branch near the base.

Dimensions.—Shell 0.08 long, 0.1 broad; horns 0.05 to 0.07 long, feet 0.16 long.

Shell nut-shaped, tuberculate, with sharp sagittal stricture. Pores large, irregular roundish; two or three pairs of larger pores on each side of the ring. Basal plate with three large triangular pores. Three horns simple, about as long as the shell, the apical straight, the two frontal elegantly curved. Three feet somewhat longer, slender, curved, with a recurved branch near the base, repeatedly forked at the distal end.

Shell nut-shaped, spiny, with deep sagittal stricture. Pores irregular polygonal or roundish. Basal plate with two large semicircular pores. Three horns slender, simple, about half as long as the shell. Three feet of the same length, slender, divergent, irregularly branched like coral.

Shell subspherical, smooth, without external sagittal stricture. Pores subregular circular. Basal plate with four large pores (?). Three horns simple, straight, divergent, spindle-shaped, half {1032}as long as the shell. Caudal foot of the same form, twice as long. Two pectoral feet cylindrical, curved, twice as long as the shell, palmate, divided at the distal end into five short fingers.

Shell nut-shaped, papillate, with deep sagittal stricture. Pores irregular roundish. Basal plate with six pores (?). Apical horn short, conical, two frontal horns very large, curved, widely divergent, longer than the shell. Three feet of about the same length, irregularly branched.

Dimensions.—Shell 0.08 long, 0.12 broad; lateral horns and feet 0.15 to 0.2 long.

Subgenus 3. Triospyridium, Haeckel.

Shell nut-shaped, smooth, compressed, with broad sagittal ring. Pores irregular roundish; one pair of very large pores on each side of the ring. Basal plate with four large collar pores. Three horns and three feet short, divergent, slightly curved, about half as long as the shell, irregularly branched. (In general form very similar to Elaphospyris damaecornis, Pl. 84, fig. 10, with which I formerly confounded it.)

Shell subspherical, with deep sagittal stricture. Pores irregular roundish; three pairs of larger pores on both sides of the ring. Basal plate with two large collar pores. Three horns about half as long as the shell, with few irregular terminal branches. (Beginning of a cupola.) Three feet strong, cylindrical, twice as long as the shell, richly branched, arborescent.

Genus 443. Tristylospyris,^[61] Haeckel, 1881, Prodromus, p. 441.

The genus Tristylospyris exhibits in general the same structure as the typical genus Tripospyris, its ancestral form. It differs from the latter in the absence of the apical {1033}horn, which is completely reduced, and may therefore be regarded as the simplest prototype of all tripodal Cyrtellaria without a horn.

Subgenus 1. Tristylospyrula, Haeckel.

Shell companulate, smooth, with slight sagittal stricture. Pores irregular roundish, three pairs of larger annular pores on each side of the broad ring. Basal plate with four large collar pores. Feet half as long as the shell, slightly divergent, straight, prismatic, with a broad, hand-like, radially striped plate at the distal end.

Shell nut-shaped, smooth, with sharp sagittal stricture. Pores very small and numerous, circular; two pairs of larger pores on both sides of the ring. Basal plate with four large pores (?). Feet about half as long as the shell, angular, shovel-shaped, straight, parallel, vertical.

Shell nut-shaped, rough, with deep sagittal stricture. Pores small, subregular circular. Basal plate with three large pores. Feet about as long as the shell, slender, straight, divergent, with a spinulate knob at the thickened distal end.

Ceratospyris triceros, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxi. fig. 5.

Shell nut-shaped, tuberculate, without external sagittal stricture. Pores circular, not numerous. Basal plate with four large collar pores. Feet large, cylindrical, three to four times as long as the shell, strongly curved and divergent.

Subgenus 2. Tristylospyrium, Haeckel.

Shell subspherical, rough, with slight sagittal stricture. Pores subregular circular. Basal plate with three large collar pores. Feet cylindrical, three to four times as long as the shell, strongly curved and divergent, at the distal end forked, with two short (sometimes ramified) branches.

Shell subspherical, tuberculate, with a prominent sagittal ring. Pores irregular roundish. Basal plate with three large pores. Feet large, straight, widely divergent, about twice as long as the shell, prismatic, irregularly branched. (Compare the following species.)

Shell subovate, tuberculate, very similar to the preceding species. It differs from this in the very different size of the irregular pores and the greater breadth of the pedal branches. The basal plate in a complete specimen (observed afterwards from the base) exhibited four large collar pores of the usual form, whilst in the similar preceding species it had three pores. In the similar Tripodiscium sphærocephalum (Pl. 52, fig. 21) the basal mouth is quite simple and open.

Genus 444. Cephalospyris,^[62] Haeckel, 1881, Prodromus, p. 441 (sensu emend.).

Definition.—Zygospyrida with three basal feet and two large apical openings or coryphal holes, one on each side of the ring-apex. No true horns.

The genus Cephalospyris comprises some few Tripospyrida of very peculiar shape, differing from all other Zygospyrida in the possession of two large apical holes or coryphal apertures, lying on each side of a latticed sagittal septum, which is formed by the upper part of the sagittal ring. The sagittal stricture is deep, with a complete {1035}primary ring. The vertical axis of the slender ovate shell is much greater than the transverse. The network is very delicate, with very small and numerous triangular or polygonal pores. The central capsule encloses peculiar concrements (Pl. 96, fig. 28).

Shell slender ovate, two and a half times as long as broad, with deep sagittal stricture and complete ring. Network very delicate, with very small and numerous, irregular polygonal pores. The two large apical holes are separated by a latticed triangular sagittal septum, the apex of which represents a rudimentary horn. Basal plate with two large collar holes. Three feet slightly curved, divergent, about half as long as the breadth of the shell; the caudal foot slender, much thinner than the two stout pyramidal pectoral feet.

Shell slender, ovate, twice as long as broad, with deep sagittal stricture and complete ring. Network very delicate, with very small and numerous triangular pores (on both poles intermingled with irregular polygonal pores). The two large apical holes are separated by a latticed triangular sagittal septum, the upper edge of which is concave and bears two rudimentary horns. Basal plate with four large collar holes. Three feet latticed, slightly curved, convergent, scarcely one-eighth as long as the breadth of the shell. The central capsule filled up by concrements.

Shell ovate, one and a half times as long as broad, with deep sagittal stricture and complete ring. Network very delicate and regular, with small triangular pores of equal size. The two large apical holes are separated by a latticed semilunar septum, the upper edge of which is concave, and bears two rudimentary horns. Basal plate with three large collar holes (?). Three feet latticed, conical, nearly parallel and vertical (the caudal curved), about half as long as the breadth of the shell. The ovate central capsule contains peculiar amyloidal concentric concrements.

Subfamily 2. Dipospyrida, Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida dipoda, with two descending lateral basal feet (probably corresponding to the pectoral feet of Cortina).

Genus 445. Dipospyris,^[63] Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida with two simple free basal feet and one apical horn.

The genus Dipospyris and the following five genera represent together the interesting subfamily of Dipospyrida, which always bear two opposite lateral feet only. Therefore in this bipedal group the biradial or bilateral type of the Spyroidea is particularly expressed. Such bipedal forms never occur in the Cyrtoidea. The topographical relation of the two lateral feet to the rods of the collar-plate, and to the cortinar pores separated by these, leaves no doubt that they correspond to the pectoral feet of Cortina and Tripospyris, and therefore that the Dipospyrida have originated from the Tripospyrida by loss of the caudal foot. Dipospyris is the simplest form of the Dipospyrida, with two simple free feet.

Shell thorax-shaped, smooth, with deep sagittal stricture, two vaulted bosoms, and subregular circular pores. Basal plate with two large collar pores only. Horn and feet equal, conical, straight, about as long as the shell; the feet widely divergent.

Ceratospyris mystax, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 6.

Shell elliptical spinulate, with slight collar stricture and large subregular circular pores. Basal plate with three pores (?) Horn small conical, oblique, shorter than the shell. Feet slender conical, longer than the shell, slightly curved, divergent. At the base of the columella, between the two feet, a small rudiment of the last caudal foot is visible.

Shell box-shaped, subcubical, papillate, without external sagittal stricture, with numerous subregular circular pores. Basal plate with three very large collar pores, surrounded by a circle of smaller pores. Apical horn short and thick, scarcely half as long as the shell. Feet of the same form, longer than the shell, widely divergent.

Shell elliptical, compressed, nodose, with deep sagittal stricture and irregular roundish pores. Basal plate with three pores (?). Apical horn stout, conical, twice to four times as long as the shell (often much longer than in the figured specimen). Feet scarcely longer then the shell, cylindrical, slightly curved towards one another.

Dimensions.—Shell 0.08 long, 0.12 broad; horn 0.2 to 0.3 long, feet 0.1 to 0.15 long.

Shell subspherical, without external sagittal stricture, with small circular pores. Basal plate with four pores. Apical horn small, conical, shorter than the shell. Feet three to four times as long as the shell, cylindrical, irregularly curved, very variable in size and form.

Dimensions.—Shell 0.08 long, 0.1 broad; horn 0.02 to 0.04 long, feet 0.2 to 0.3 long.

Shell violin-shaped, thorny, with deep sagittal stricture and irregular roundish pores. Basal plate with four collar pores. Horn straight, conical, about as long as the shell. Feet twice as long, cylindrical, markedly divergent, S-shaped, curved.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms; also fossil in Barbados.

Shell nut-shaped, tuberculate, with subregular circular pores. Basal plate with four larger and a circle of six to ten smaller pores. Horn cylindrical, straight, two to three times as long as the shell. Feet three to five times as long as the shell, cylindrical, semicircular, with convergent and crossed distal ends. (If these ends grow together, Gamospyris arises.)

Dimensions.—Shell 0.08 long, 0.11 broad; horn 0.15 to 0.2 long, feet 0.2 to 0.4 long.

Genus 446. Brachiospyris,^[64] Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida with two simple free basal feet, without apical horn.

The genus Brachiospyris differs from the preceding Dipospyris, its ancestral form, only in the absence of the reduced apical horn, and therefore bears to it a similar {1038}relation to that which the hornless Tristylospyris, among the Tripospyrida, bears to the horned Tripospyris. Brachiospyris may therefore also be derived from Tristylospyris by loss of the caudal foot.

Ceratospyris ocellata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 5.

Shell nut-shaped, thorny, with slight sagittal stricture and irregular roundish pores. Basal plate with four large and four alternate pairs of smaller pores. Two feet cylindrical, straight, divergent, two to three times as long as the shell.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms; also fossil in Barbados.

? Ceratospyris diacantha, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 303.

Shell nut-shaped, tuberculate, compressed in the sagittal axis, convex on the frontal face, concave on the sagittal face, with a slight sagittal stricture; with large irregular roundish pores. Basal plate with three very large pores. Two feet cylindrical, curved, S-shaped, about twice as long as the shell.

Habitat.—Western Tropical Pacific (Philippine Sea), Station 206, depth 2100 fathoms.

Genus 447. Dendrospyris,^[65] Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida with two free lateral feet, forked or branched like a tree. Apex with a horn.

The genus Dendrospyris differs from its ancestral form Dipospyris in the ramification of the two large lateral feet, which descend from the base of the shell, and are usually very large and stout, sometimes simply forked.

Ceratospyris stylophora, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 10.

Shell nut-shaped, thorny, with subregular circular pores. Basal plate with four pores. Apical horn and the two divergent feet straight, cylindrical, larger than the shell, forked at the distal end. {1039}(The size and number of the fork-branches is variable; the horn is sometimes simple. In some specimens a rudimentary remnant of the lost caudal foot is visible.)

Ceratospyris dirrhiza, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 9.

Shell nut-shaped, spiny, very similar to the preceding species. It differs from that mainly in the growth of the cylindrical feet, which are not straight and divergent, but more or less curved and convergent; their distal ends are sometimes simply forked, sometimes repeatedly dichotomous. The size and form of the apical horn are also very variable.

Cladospyris bibrachiata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. xxi. fig. 7.

Shell nut-shaped, smooth, with sharp stricture and numerous very small circular pores. Apical horn and the two feet very large and stout, straight, prismatic, with irregular lateral branches on their edges, twice to four times as long as the shell (The horn in the Ehrenberg's figure is broken off.) This species is closely allied to Tripospyris tribrachiata.

Shell subspherical, tuberculate, with irregularly roundish pores. Basal plate with two large pores. Apical horn simple, conical, as long as the shell. Feet cylindrical, twice as long, in the proximal half parallel, vertical, in the distal half with two stout divergent equal fork-branches, one of which is directed dorsally, the other ventrally.

Dimensions.—Shell 0.07 long, 0.08 broad; horn 0.06 long, feet 0.1 to 0.15 long.

Shell subspherical, rough, with subregular circular pores. Basal plate with three pores (?). Apical horn simple, conical, half as long as the shell. Feet cylindrical twice to three times as long as the shell, semicircular, with a strong conical tooth in the middle of their outer convex edge; their distal ends convergent, divided into a bunch of numerous short irregular branches.

Dimensions.—Shell 0.7 long, 0.08 broad; horn 0.03 long, feet 0.15 to 0.25 long.

Shell nut-shaped, spiny, with irregular roundish pores. Basal plate with three pairs of pores. Apical horn cylindrical, spinulate, twice to three times as long as the shell. Feet as long as the horn, S-shaped, widely divergent, irregularly branched, with widely distant pointed branches.

Shell nut-shaped, tuberculate, with subregular circular pores. Basal plate with four central larger and ten to twelve peripheral smaller pores. Apical horn cylindrical, twice as long as the shell, in the distal half spinulate or tuberculate. Feet about three times as long as the shell, cylindrical, nearly vertical, in the distal half irregularly branched, with dense bunches of aggregated blunt branches.

Genus 448. Dorcadospyris,^[66] Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida with two free lateral feet armed with a series of secondary spines. Apex with a horn.

The genus Dorcadospyris and the closely allied Stephanospyris differ from the other Dipospyrida in the development of a series of secondary spines on the convex outer margin of the two large curved lateral feet, which therefore appear semipinnate. In some species this peculiar armature attains an extraordinary size, whilst the shell itself is very small, as in Dorcadospyris dinoceras (Pl. 85, fig. 4).

Shell subspherical, tuberculate with small regular circular pores. Basal plate with four larger pores. Apical horn three to four times as long as the shell, slender conical, smooth. Feet more or less convexly curved towards one another; the distal ends not crossed. In the convex edge of each arm a series of five to ten smooth conical teeth, not longer than the shell. This common species is very variable and often asymmetrical; the figured specimen is an asymmetrical one, in which the two arms exhibit different curves; in the normal form both arms have the same curve, now more, now less convex.

Shell subspherical, tuberculate, with small regular circular pores. Basal plate with four larger pores. Apical horn four to six times as long as the shell, straight, cylindrical, smooth. Feet of the same length, crescentic or nearly semicircular, with crossed distal ends. On the convex edge of each foot a series of twelve to fifteen smooth conical teeth, partly longer than the shell. (Very variable in size and curvature of the feet, and number of their teeth.)

Shell subspherical spinulate, nearly of the same shape as in the preceding species, but with a short conical horn (scarcely as long as the shell); the feet are much mere slender, crescentic, and bear twenty to thirty smaller smooth conical teeth (shorter than the shell). The distal ends of the feet are crossed.

Dimensions.—Shell 0.08 long, 0.09 broad; horn 0.06 long, feet 0.03 to 0.06 long.

Shell subspherical, smooth, very similar to that of the two preceding species. Horn small conical, about as long as the shell. Feet more than semicircular, more strongly curved than in any other species, each with four to eight small conical teeth, shorter than the shell; distal ends crossed. (In this species also, besides the normal symmetrical form, there often occurs an asymmetrical form of the two feet; one of these frequent anomalies is shown in fig. 7.)

Shell subspherical, tuberculate, with subregular circular pores. Basal plate with four larger central and eight to twelve smaller peripheral pores. Horn about as long as the shell, in the basal half prismatic, smooth, in the distal half ovate or strobiliform, spiny. Feet very large and strongly curved, together nearly heart-shaped, four to six times as long as the shell. Each foot bears on its outer convex side a series of fifteen to twenty or more strong conical teeth, which are again spinulate, perpendicular to the foot, and longer than the shell.

Dimensions.—Shell 0.08 long, 0.09 broad; horn 0.07 long, feet 0.3 to 0.5 long.

Genus 449. Gamospyris,^[67] Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida with two simple lateral feet, forming a ring by union.

The genus Gamospyris and the similar Stephanospyris differ from all other Spyroidea in the possession of a large basal ring, placed in the frontal plane of the shell. This ring has been produced by concrescence of the distal ends of the two large curved lateral feet of Dipospyris.

Shell subspherical, tuberculate, with subregular circular pores. Basal plate with four larger collar pores. Apical horn pyramidal, about as long as the shell. The connected feet form together a circular or nearly circular smooth ring, the diameter of which is three to four times as great as that of the shell.

Dimensions.—Shell 0.08 long, 0.09 broad; diameter of the arm-ring 0.25 to 0.33.

Shell nut-shaped, tuberculate, with subregular circular pores. Basal plate with four large central and a circle of eight to twelve small peripheral pores. Apical horn conical, twice as long as the shell. The connected arms form together an elliptical smooth ring, which is five times as long and three times as broad as the shell.

Genus 450. Stephanospyris,^[68] Haeckel, 1881, Prodromus, p. 441.

Definition.—Zygospyrida with two lateral feet bearing a series of secondary spines and forming a ring by union.

The genus Stephanospyris exhibits the same peculiar armature of the semipinnate lateral feet as its ancestral genus Dorcadospyris, but differs from it in the concrescence of the distal ends of the feet, to form a complete foot-ring. The former therefore bears to the latter the same relation that Gamospyris does to Dipospyris.

Shell subspherical, tuberculate, with small regular circular pores. Basal plate with four larger pores. Apical horn cylindrical, three times as long as the shell, with three to four verticils {1043}of teeth. The connected feet form a heart-shaped ring, four times as long and three times as broad as the shell. Each foot bears on the outer convex edge four to six stout conical teeth, shorter than the shell. Distal ends crossed and prominent.

Shell nut-shaped, tuberculate, with subregular circular pores. Basal plate with numerous small pores. Apical horn cylindrical, four to six times as long as the shell, with six to ten verticils of teeth. The connected feet form a circular ring, the diameter of which is four times as great as that of the shell. Each foot bears ten to twelve conical teeth, about as long as the shell. Distal ends not crossed and not prominent.

Shell subspherical, tuberculate, with regular circular pores. Basal plate with numerous small pores. Apical horn cylindrical, twice as long as the shell, with eight verticils of teeth. The connected feet form an ovate ring, which is three times as long and two and a half times as broad as the shell. Each foot bears eight conical spinulate teeth, about as long as the shell. The crossed and prominent distal ends bear two parallel vertical teeth.

Subfamily 3. Tetraspyrida, Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida tetrapoda, with four descending basal feet, two of which are opposite in the sagittal plane (an odd caudal and an odd sternal foot), whilst the two others are paired lateral or pectoral feet.

Genus 451. Tetraspyris,^[69] Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida with four basal feet crossed in pairs (two sagittal and two lateral). Apex with a horn.

The genus Tetraspyris and the following closely allied Tessarospyris represent together the small subfamily of Tetraspyrida, characterised by the possession of four descending basal feet, three of which correspond to the three original feet of the {1044}ancestral genera Cortina and Tripospyris, whilst the fourth in an odd anterior or sternal foot, produced by anterior prolongation of the basilar segment of the sagittal ring. Here, therefore, two opposed feet lie in the sagittal plane (a caudal and a sternal foot), whilst the two others are the paired lateral or pectoral feet, as also in Stephanium and Stephaniscus, p. 965. The Tetraspyrida ought not to be confounded with the Therospyrida (sixth subfamily), in which the four feet have another signification.

Subgenus 1. Tetrarrhabda, Haeckel, 1881, p. 429.

Shell nut-shaped, tuberculate, with deep sagittal stricture and small roundish pores; three pairs of larger pores on each side of the ring. Basal plate with four large collar pores. Apical horn stout conical, half as long as the shell. Two pectoral feet somewhat longer than the two sagittal feet, one and a half times as long as the shell. All four feet straight, three-sided prismatic, strongly divergent.

Dimensions.—Shell 0.08 long, 0.12 broad; horn 0.04 long, feet 0.08 to 0.12 long.

Shell nearly cubical, smooth, with slight sagittal stricture and small polygonal pores; some larger pores on both sides of the ring. Basal plate with four large collar pores. Apical horn and the four feet of equal size and form, about as long as the shell, cylindrical in the basal, spindle shaped in the distal half.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms; also fossil in Barbados.

Subgenus 2. Tetracorethra, Haeckel, 1831, Prodromus, p. 429.

Tetracorethra mirabilis, Haeckel, 1881, Prodromus, p. 439, and Atlas, loc. cit.

Shell campanulate, tuberculate, with deep sagittal stricture and irregular polygonal pores; two pairs of larger pores at the flattened occipital face (fig. 20). Basal plate with four large collar pores. Apical horn very long, thirty to forty times as long as the shell, slender three-sided prismatic, straight, at the distal end irregularly branched, besom-shaped. Four basal feet half as {1045}thick as the horn, eight to twelve times as long as the shell, bristle-shaped, irregularly curved and branched, divergent, at the distal end besom-shaped. Central capsule very large; the enclosed small campanulate part sends out through the four collar pores four very long club-shaped basal lobes, half as long as the feet; each lobe contains a large oil-globule (fig. 19).

Dimensions.—Shell 0.036 diameter; horn 1 to 1.5 mm. long, feet 0.3 to 0.4 long.

Shell campanulate, smooth, very similar to that of the preceding species, but differing in the following characters:—the two inferior occipital pores are four times (in the preceding twice) as large as the two superior; the apical horn bears at its distal end only three simple branches; the sternal foot is smaller than the three others, arises higher, is more divergent and curved, and bears at its base a large horizontal conical spur.

Shell campanulate, rough, very similar to the two preceding species, but differing in the following characters:—the four occipital pores are of nearly equal size; the apical horn is simple, not branched; the four feet are forked near the base, so that apparently eight feet diverge, each in the distal half richly branched, besom-shaped.

Genus 452. Tessarospyris,^[70] Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida with four basal feet crossed in pairs (two sagittal and two lateral). Apex without horn.

The genus Tessarospyris differs from the preceding Tetraspyris, its ancestral genus, in the absence of the apical horn, and therefore bears to it the same relation that Tristylospyris does to Tripospyris.

Clathrobursa dictyopus, Haeckel, 1881, Prodromus, p. 439, and Atlas, pl. liii. fig. 8.

Shell nearly ovate, strongly compressed, smooth, one and a half times as long as broad, with deep sagittal stricture in the basal half. Pores very small and numerous, irregularly roundish. Basal plate with four very large triangular holes, two larger (posterior) cardinal, and two smaller (anterior) {1046}jugular pores; above the latter (on the frontal face) two large mental pores. Two pectoral feet large, half as long as the shell, at the base fenestrated, vertical, and parallel. Two sagittal feet much smaller, nearly horizontal, pyramidal (the caudal larger than the sternal foot). Two longitudinal pectoral ribs arise on the frontal face.

Dimensions.—Shell 0.21 long, 0.14 broad; lateral feet 0.1, sagittal feet 0.02.

Shell nut-shaped, papillate, with deep sagittal stricture. Pores irregular roundish, on both sides of the ring three to six times as large as on the lateral sides. Basal plate with four large pores. Two pectoral feet cylindrical curved, twice as long as the shell and as the two sagittal feet; the caudal is much stronger than the sternal foot.

Dimensions.—Shell 0.06 long, 0.09 broad; lateral feet 0.1, sagittal feet 0.05 long.

Petalospyris seminulum, Stöhr, 1880, Palæontogr., vol. xxvi. pl. iii. fig. 12.

Shell subspherical, smooth, with slight sagittal stricture and small circular pores; some larger pores on both sides of the ring. Basal plate with two large (lateral) pores only. Four feet nearly equal, short, conical, divergent, scarcely one-fourth as long as the shell.

Subfamily 4. Hexaspyrida, Haeckel.

Definition.—Zygospyrida hexapoda, with six descending basal feet; three of these are primary (one odd caudal and two paired pectoral feet), the other three are secondary, opposed diametrically to the former and alternating with them (one odd sternal and two paired tergal feet).

Genus 453. Hexaspyris,^[71] n. gen.

The genus Hexaspyris and the two following closely allied genera represent together the peculiar subfamily of Hexaspyrida, and differ from the other Zygospyrida in the possession of six descending basal feet; three of these are the three original, perradial, or primary basal feet of Cortina, Cortiniscus, Plagoniscus, Plectaniscus, Tripospyris, &c.; the other three, usually opposed to the former diametrically, are {1047}secondary or interradial; an odd sternal foot (opposed to the odd caudal) and two paired tergal feet (opposed to the two paired pectoral).

Subgenus 1. Hexaspyridium, Haeckel.

Shell nut-shaped, smooth, with deep sagittal stricture and irregular polygonal pores; on each side of the stricture two pairs of larger square annular pores. Basal plate also with four larger collar pores. Apical horn twice as long as the shell, conical. Three primary feet (the apical and the two pectoral) slender, curved, as long as the horn; three secondary feet (the sternal and the two tergal) are half as long as the former and more highly inserted; all six feet strongly divergent, cylindrical, pointed.

Dimensions.—Shell 0.06 long, 0.09 broad; horn 0.15 long, feet 0.08 to 0.14 long.

Ceratospyris setigera, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 11.

Ceratospyris setigera, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 539, Taf. xxxii. figs. 11a, 11b.

Shell nut-shaped, tuberculate, with a complete internal sagittal ring and numerous small circular pores. Basal plate with four larger central and a circle of twelve to twenty smaller peripheral pores. Apical horn half as long as the shell, bristle-shaped. Three primary feet longer and more deeply inserted than the three secondary feet; all six feet strongly divergent, bristle-shaped, shorter than the shell.

Dimensions.—Shell 0.06 long, 0.09 broad; horn 0.03 long; primary feet 0.05, secondary 0.02 long.

Ceratospyris triomma, Bütschli (non Ehrenberg), 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 539, Taf. xxxii. fig. 12, a, b.

Shell nut-shaped, spinulate, with a complete internal sagittal ring and subregular circular pores. Basal plate with twelve pores (four larger central and eight smaller peripheral). Apical horn stout, oblique, as long as the shell. Six feet of equal length, slightly divergent, nearly vertical, slender, three to four times as long as the shell.

Petalospyris spinosa, Stöhr, 1880, Palæontogr., vol. xxvi. p. 98, Taf. iii. fig. 14.

Shell subspherical, smooth, with slight sagittal stricture and irregular polygonal pores; on each side of the stricture two pairs of larger pores. Basal plate with two large pores only. Apical horn short, pyramidal, three primary feet half as long as the shell and twice as long as the three secondary feet. All six feet pyramidal, slightly divergent.

Petalospyris ophirensis, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. ix. fig. 24.

Shell nut-shaped, with deep sagittal stricture and numerous irregular roundish pores; two pairs of larger pores on each side of the stricture. Apical horn short, curved. Six feet equal, divergent, straight, slender, about as long as the shell.

Subgenus 2. Hexacorethra, Haeckel.

Hexacorethra magica, Haeckel, 1882, Manuscript.

Shell campanulate, smooth, with sharp sagittal stricture and irregular roundish pores. Basal plate with six larger collar pores. Apical horn very long and thin, three-sided prismatic, straight, ten to twenty times as long as the shell, branched at the distal end. Six feet thinner, bristle-shaped, six to eight times as long as the shell, divergent, irregularly curved, in the distal part branched, besom-shaped; the sternal foot at its base with a large conical horizontal spur.

Dimensions.—Shell 0.034 diameter; horn 0.4 to 0.8 long, feet 0.2 to 0.3 long.

Ceratospyris articulata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 4.

Shell nut-shaped, tuberculate, with deep sagittal stricture and small irregular roundish pores. Basal plate with six pores (?). Apical horn conical, longer than the shell. Six feet very large, thick {1049}cylindrical, divergent, three to four times as long as the shell, with few irregular lateral branches (often much more developed than in Ehrenberg's figure).

Genus 454. Liriospyris,^[72] Haeckel, 1881, Prodromus, p. 443.

The genus Liriospyris differs from the preceding Hexaspyris, its ancestral form, in the possession of three coryphal horns (one odd apical in the middle, and two paired frontal horns on each side of it); it therefore bears to the latter the same relation that Triceraspyris does to Tripospyris.

Shell subspherical, smooth, with slight sagittal stricture and irregular roundish pores; two to three pairs of large annular pores on each side of the stricture. Basal plate with four large collar pores. Three horns and six feet nearly of the same size and of similar form, conical, divergent, about one-third as long as the shell.

Dictyospyris clathrus, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 25.

Dictyospyris clathrata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. xix. fig. 7.

Dictyospyris clathrata, Bütschli, 1882, Zeitschr. f. Wiss. Zool., vol. xxxvi. pp. 506, 539; Taf. xxxii. figs. 10a, 10b.

Petalospyris clathrus, Haeckel, 1862, Monogr. d. Radiol., p. 295.

Shell campanulate or nearly spherical, smooth, with slight sagittal stricture. Three pairs of large annular pores on each side of the stricture; a few smaller irregular pores on the lateral sides. Basal plate with six large collar pores (Bütschli, loc. cit., fig. 10a). Three horns and six feet nearly of the same size and form; short, conical, slightly divergent or nearly parallel, shorter than half the ring. (The size of the nine appendages is in this common species rather variable; sometimes they are rudimentary, at other times much stronger than in the good figure of Bütschli.)

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific; also fossil in Barbados and Sicily.

Shell nut-shaped, nodose, with deep sagittal stricture and small circular pores; two pairs of larger pores on each side of the stricture. Basal plate with four larger central and eight smaller peripheral pores. Apical horn conical, as long as the shell and twice as long as the two curved frontal horns. Three primary feet twice as long as the shell and as the three secondary feet, which are more highly inserted. All six feet slender curved, divergent.

Dimensions.—Shell 0.07 long, 0.11 broad; horn and secondary feet 0.08 long, primary feet 0.15 long.

Ceratospyris turrita, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 1.

Shell ovate, campanulate, smooth, with sharp sagittal stricture and irregular roundish pores; three to four pairs of larger pores on each side of the stricture. Basal plate with four large collar pores. Three horns short and stout, conical, fenestrated at the base. Six feet slender, conical, nearly vertical, of equal size, only one-third as long as the shell.

Shell nut-shaped, tuberculate, with distinct sagittal stricture and irregular roundish pores. Basal plate with six larger and twelve smaller pores. Three horns conical, the apical as long as the shell and twice as long as the curved frontal horns. Two pectoral feet cylindrical, very large, curved, divergent, about three times as long as the shell and as the four other feet, which are conical.

Dimensions.—Shell 0.08 long, 0.12 broad; apical horn 0.08, frontal horns 0.05 long; length of the two pectoral feet 0.2, of the four others 0.06.

Genus 455. Cantharospyris,^[73] n. gen.

The genus Cantharospyris differs from the preceding two hexapodal genera in the absence of horns on the coryphal face, and has therefore the same relation to them that the hornless Tristylospyris bears to the one-horned Tripospyris and the three-horned Triceraspyris.

Shell nut-shaped, with deep sagittal stricture and irregular roundish pores. Basal plate with six larger pores. Six feet of different sizes, cylindrical, curved; three primary feet (one caudal and two pectoral) about as long as the shell and twice as long as the three secondary feet.

Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms; Central Pacific, Station 268, depth 2900 fathoms.

Ceratospyris ateuchus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxi. fig. 4.

Shell nut-shaped, tuberculate, with slight sagittal stricture and unequal circular pores. Basal plate with six larger pores. The two pectoral feet very large and stout, four to six times as long as the shell, widely divergent, curved. The four other feet much smaller and thinner, about as long as the shell.

Dimensions.—Shell 0.06 long, 0.08 broad; length of the two larger feet 0.2 to 0.3, of the four smaller 0.05 to 0.07.

Ceratospyris radicata, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 37.

Haliomma radicatum, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 83.

Petalospyris radicata, Haeckel, 1862, Monogr. d. Radiol., p. 295.

Petalospyris radicata, Stöhr, 1880, Palæontogr., vol xxvi. p. 79, Taf. iii. fig. 11.

Shell nut-shaped, smooth, with slight sagittal stricture and irregular roundish pores; two larger pores on each side of the ring. Basal plate with six pores (?). Six feet of equal size and similar form, conical, divergent, slightly curved, shorter than half the ring.

Platybursa compressa, Haeckel, 1881, Prodromus, p. 429; Atlas, pl. 53, fig. 7.

Shell smooth, nearly discoidal circular, markedly compressed in the sagittal direction, with slight basal stricture. Pores very numerous, irregular polygonal, with thin bars. Basal plate with four very large pores. Six feet short, conical, nearly horizontally expanded. Two sagittal feet (caudal {1052}and sternal) larger, about half as long as the shell (shortened in the figure). The two sternal feet larger than the two small or rudimentary tergal feet.

Subfamily 5. Pentaspyrida, Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida pentapoda, with five descending basal feet, one odd caudal foot, and two pairs of lateral feet (two anterior or pectoral, and two posterior or tergal feet).

Genus 456. Clathrospyris,^[74] Haeckel, 1881, Prodromus, p. 442.

The genus Clathrospyris and the two following closely allied genera represent together the small subfamily of Pentaspyrida, differing from the other Zygospyrida in the possession of five descending feet on the basal face. Three of these are the primary cortinar feet (of Cortiniscus, Plagoniscus, Tripospyris, &c.), whilst the two others are secondary tergal feet. The Pentaspyrida may therefore be probably derived from the Hexaspyrida by loss of the odd anterior or sternal foot.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores irregular roundish. Basal plate with six pores (?). Two pectoral feet very large, twice as long as the shell, cylindrical, curved. Two tergal feet half as long and thick as the pectoral. Caudal foot and apical horn straight, conical, half as long as the shell.

Dimensions.—Shell 0.07 long, 0.09 broad; horn and odd caudal foot 0.04 long; pectoral feet 0.16, tergal 0.08 long.

Shell four-sided pyramidal, truncate, thorny, with a slight sagittal stricture. Pores very large, polygonal roundish. Two pairs of large pores on each side of the ring (at the frontal and the occipital plate). Lateral pores more numerous. Basal plate with four large pores. The four edges of the pyramid are prolonged into four short pyramidal divergent lateral feet (one-third as {1053}long as the shell). Caudal foot short. Horn at the apex of the truncate pyramid with two lateral teeth.

Shell nearly cubical, smooth, with slight sagittal stricture. Pores roundish; three pairs of larger pores on each side of the ring. Basal plate with six large pores. Five feet of equal length, slender, spindle-shaped, about as long as the shell, divergent. Apical horn conical, and half as long as the feet.

Genus 457. Aegospyris,^[75] Haeckel, 1881, Prodromus, p. 442.

The genus Aegospyris differs from the preceding Clathrospyris, its ancestral form, in the possession of three horns on the coryphal face (one odd apical, and two paired frontal horns on each side), and therefore bears to the latter the same relation that Triceraspyris does to Tripospyris, and Liriospyris to Hexaspyris.

Shell nut-shaped, tuberculate, with slight sagittal stricture. Pores subregular circular. Basal plate with four large collar pores. Three horns and five feet all of equal size and similar form, slender conical, slightly curved, widely divergent, about as long as the shell.

Shell nearly cubical, smooth, with slight sagittal stricture. Pores subregular circular; two pairs of larger pores on each side of the ring. Basal plate with four large pores. Two paired horns and four paired feet of equal size and similar form, S-shaped curved, twice as long as the shell. Odd horn and odd feet half as long, straight, conical.

Dimensions.—Shell 0.08 long, 0.09 broad; six paired spines 0.2 long, two odd spines 0.1 long.

Ceratospyris longibarba, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxi. figs. 1, 2.

Shell nut-shaped, tuberculate, with slight sagittal stricture. Pores subregular circular. Basal plate with four larger central, and eight smaller peripheral pores. Apical horn and caudal foot short, straight, conical; two frontal horns longer, curved; four paired feet slender, curved, twice as long as the shell.

Dimensions.—Shell 0.06 long, 0.08 broad; paired horns 0.03 long, paired feet 0.1 long.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores irregular roundish. Basal plate with three large pores. Apical horn and caudal foot short, straight, spindle-shaped; two frontal horns as long as the shell, strongly curved; four paired feet also curved, at the distal end forked, divergent; the tergal thinner and as long as the shell, the pectoral thicker and twice as long.

Shell nut-shaped, papillate, with sharp sagittal stricture. Pores irregular roundish, two pairs of larger pores on each side of the ring. Basal plate with six large pores. Eight spines all straight, subvertical and nearly parallel, cylindro-conical. Two frontal horns and two tergal feet about as long as the shell; odd horn shorter; odd foot longer. Two pectoral feet twice as long as the shell, club-shaped, with a spinulate knob at the distal end.

Genus 458. Pentaspyris,^[76] Haeckel, 1881, Prodromus, p. 442.

The genus Pentaspyris differs from the two preceding genera in the absence of any coryphal horn, and represents therefore the pentapodal form among the hornless Zygospyrida.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores irregular roundish, two pairs of larger pores on each side of the ring. Basal plate with four larger pores. All five feet {1055}cylindrical, S-shaped curved, strongly divergent, with few short branches, the two pectoral feet twice as long as the shell and the two tergal feet; odd caudal foot shorter.

Dimensions.—Shell 0.08 long, 0.13 broad; pectoral feet 0.2 long, tergal feet 0.1, caudal foot 0.06.

Shell subspherical, smooth, with slight sagittal stricture. Pores small, regular circular. Basal plate with six large pores (?). All five feet equal, cylindrical, C-shaped curved, slightly divergent, about as long as the shell.

Subfamily 6. Therospyrida, Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida tetrapoda with two pairs of descending basal feet, one pair corresponding to the anterior or pectoral, the other pair to the posterior or tergal feet of the Hexaspyrida.

Genus 459. Zygospyris,^[77] Haeckel, 1881, Prodromus, p. 442.

The genus Zygospyris and the following three genera represent together the peculiar subfamily of Therospyrida. These always possess four basal feet, like the Tetraspyrida; but whilst in the latter group two feet are sagittal, and two lateral, in the Therospyrida there are no sagittal feet at all, but the four feet are opposed in two lateral pairs; the anterior pair corresponds to the pectoral, the posterior to the tergal feet of the Hexaspyrida and Pentaspyrida; from these latter the Therospyrida have been derived by loss of the sagittal feet.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores irregular roundish, on each side of the ring two pairs of larger pores. Apical horn conical, straight. Four feet equal, straight, divergent, conical, about as long as the shell and the horn.

Shell subspherical, rough, with slight sagittal stricture. Pores small and numerous, subregular circular; no larger annular pores. Apical horn cylindrical, half as long as the shell. Two pectoral feet somewhat smaller than the two tergal feet, about as long as the shell, slightly divergent, cylindrical. The distal ends of the feet and of the horn form an ovate, dimpled and spinulate cone.

Genus 460. Elaphospyris,^[78] Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida with two pairs of lateral feet and three coryphal horns.

The genus Elaphospyris differs from the preceding Zygospyris, its ancestral form, in the possession of three coryphal horns (one odd apical and two paired frontal horns), and therefore bears to it the same relation that Triceraspyris does to Tripospyris among the Tripospyrida.

Subgenus 1. Giraffospyris, Haeckel, 1881, Prodromus, p. 442.

Ceratospyris heptaceros, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 2.

Giraffospyris heptaceros, Haeckel, 1881, Prodromus, p. 442.

Shell nut-shaped, tuberculate, with slight sagittal stricture and subregular circular pores. Basal plate with four large pores. Apical horn small, conical, shorter than the two curved lateral horns, which are as long as the shell. Caudal and sternal feet small, conical, straight. Two pectoral feet slender, divergent, S-shaped, about as long as the shell.

Shell nut-shaped, spiny, with slight sagittal stricture and numerous small circular pores. Basal plate with four large pores. Three horns slender, simple, about as long as the shell, the middle one straight, the two lateral curved. Four feet of nearly equal size, slender, curved, divergent, simple, twice as long as the shell and the horns.

Subgenus 2. Corythospyris, Haeckel, 1881, Prodromus, p. 443.

Shell flat and broad, nearly triangular, with slight sagittal stricture and irregular roundish pores; two very large pores on the frontal and on the occipital face, opposite on both edges of the broad sagittal ring. Basal plate with four large central and several smaller lateral pores. Three horns about half as long as the shell, with two to six irregular branches. Four feet of equal size, about as long as the shell, divergent, forked, with four to six irregular terminal branches. (The shell in fig. 10 is seen from the apical side.)

Shell polyhedral, spiny, with deep sagittal stricture and a small number of large roundish pores; two pairs of large pores on each side of the ring. Basal plate with four pores. Three large horns as long as the shell arise from the apex between smaller conical spines; the middle odd horn simple, the two lateral each with a pair of branches. Two pectoral feet very large, divergent, with broad and irregular distal ramification, twice as long as the shell and as the two tergal feet, which are less branched. (Fig. 13 exhibits the shell from the dorsal side.)

Dimensions.—Shell 0.09 long, 0.11 broad; horns and smaller feet 0.07 to 0.09 long; pectoral feet 0.16 long.

Shell nut-shaped, spiny, with sharp sagittal stricture and large roundish pentagonally framed pores; three pairs of larger pores on each side of the ring. Basal plate with four larger and four alternate smaller pores. There arise from the apex, between smaller spines, three large, divergent, pyramidal horns, which are nearly as long as the shell, and connected by an arched frontal bridge. Two pectoral feet very large, divergent, prismatic, longer than the shell, and at the distal end with a bunch of thick spines. Two tergal feet half as long and thick, simple (in the figure hidden behind the large pectoral feet).

Dimensions.—Shell 0.09 long, 0.11 broad; horns and smaller feet 0.06 long, pectoral feet 0.12 long.

Genus 461. Taurospyris,^[79] Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida with two pairs of lateral feet and one pair of lateral horns.

The genus Taurospyris bears only two frontal horns in the coryphal face of the shell, and may therefore be derived from the preceding closely allied Elaphospyris by reduction and loss of the middle or apical horn.

Shell nut-shaped, thorny, with deep sagittal stricture and irregular roundish pores; three pairs of larger pores on each side of the ring. Basal plate with four large pores. Two horns cylindrical, curved, widely divergent, about as long as the shell, branched. Four feet of nearly equal length, also cylindrical and curved, divergent, somewhat longer than the shell, in the distal half branched like a deer's antler.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms; also fossil in Barbados.

Shell subspherical, smooth, with slight sagittal stricture and small circular pores. Basal plate with six larger pores. Two horns conical, curved, divergent, about as long as the shell. Two pectoral feet very large, twice as long as the shell and as the two thinner tergal feet; all four feet curved, cylindrical, divergent, pointed at the distal end.

Dimensions.—Shell 0.08 long, 0.09 broad; horns and posterior feet 0.1, anterior feet 0.2 long.

Genus 462. Therospyris,^[80] Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida with two pairs of lateral feet, without apical horn.

The genus Therospyris has two pairs of lateral feet corresponding to those of the preceding three genera, but differs from them in the complete absence of horns on the coryphal face of the shell.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores irregular, roundish. Basal plate with four longer pores. Surface covered with roundish tubercles. Four feet equal, divergent, about as long as the shell, thickened at the distal end, club-shaped, not forked.

Shell nut-shaped, mammillate, with sharp sagittal stricture. Pores large, irregularly roundish or polygonal, of somewhat different size. Basal plate with four large pores. Surface covered with hemispherical pointed mammillæ. Four feet equal, divergent, half as long as the shell, at the distal end forked, with few small branches.

Shell nearly cubical, papillate, with slight sagittal stricture. Pores irregular, roundish; on each side of the ring three pairs of larger pores (the undermost the largest). Basal plate with two large pores. Surface covered with conical papillæ. Four feet equal, divergent, about as long as the shell, with an external spur in the middle, and irregularly branched spines at the distal end.

Subfamily 7. Polyspyrida, Haeckel, 1881, Prodromus, p. 442.

Definition.—Zygospyrida polypoda, with numerous descending basal feet (at least seven to nine, usually twelve to sixteen or more).

Genus 463. Petalospyris,^[81] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Zygospyrida with numerous (seven to twelve or more) basal feet and one apical horn.

The genus Petalospyris and the following three genera form together the peculiar subfamily of Polyspyrida, differing from the other Zygospyrida in the multiplication of the radial feet, which descend from the basal face of the shell; they may therefore be also called "Zygospyrida multiradiata," and bear the closest relationship to the Archiphænida (or the "Monocyrtida multiradiata"). They differ, however, from the latter in the presence of the distinct sagittal stricture, characteristic of all Spyroidea. The number of the basal feet, which form a coronet around the margin of the basal plate, is commonly between twelve and sixteen, but often more. Their form is usually flat, lamellar, but often also more or less cylindrical or conical.

Subgenus 1. Petalospyrantha, Haeckel.

Definition.—Basal plate with two large collar pores only, separated by the base of the primary ring.

Petalospyris foveolata, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 14; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 80, Taf. xxii. fig. 10.

Shell campanulate, smooth, with distinct sagittal stricture and subregular circular pores. Basal plate with two large collar pores only. Apical horn and the eight feet slender, conical, slightly curved, about as long as the shell; feet somewhat divergent (often seven or nine instead of eight).

Dimensions.—Shell diameter 0.04 to 0.05; length of the horn and the feet 0.04 to 0.05.

Shell nut-shaped, tuberculate, with deep sagittal stricture and subregular circular pores. Basal plate with two large triangular pores only. Apical horn slender, conical, twice as long as the shell. Twelve to sixteen feet flattened, leaf-shaped, broad, slightly divergent, as long as the shell, with truncate distal end.

Dimensions.—Shell 0.06 long, 0.09 broad; horn 0.12 long, feet 0.05 to 0.07 long.

Subgenus 2. Petalospyrella, Haeckel.

Definition.—Basal plate with three large collar pores (two paired posterior cardinal, and an odd anterior sternal pore).

Shell nut-shaped, tuberculate, with sharp sagittal stricture and irregular roundish pores. Basal plate with three large pores and three alternate smaller. Apical horn stout, conical, half as long as the shell. Twelve to fifteen feet, divergent, curved, pointed, as long as the horn.

Petalospyris platyacantha, Ehrenberg, Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 80, Taf. xxii. fig. 8.

Shell campanulate, smooth, with slight sagittal stricture and small irregular roundish pores. Basal plate with three large pores (?). Apical horn very strong, three-sided pyramidal, twice as {1061}long as the shell (its edge is described by Ehrenberg as a "canaliculus.") Feet ten to twelve, flat, triangular, vertical, about as long as the shell.

Petalospyris corona, Stöhr, 1880, Palæontogr., vol. xxvi. p. 98, Taf. iii. fig. 13.

Shell nut-shaped, smooth, with slight sagittal stricture and very numerous small circular pores; on each side of the stricture three larger annular pores (the undermost the largest). Basal plate with three large pores only. Apical horn very small, conical. Feet twelve to eighteen, short conical, nearly vertical, shorter than the half shell (in my specimen from Caltanisetta much stouter than in that of Stöhr).

Subgenus 3. Petalospyrissa, Haeckel.

Definition.—Basal plate with four collar pores (two larger posterior cardinal and two smaller anterior jugular pores).

Shell nut-shaped, tuberculate, with sharp sagittal stricture and irregular, roundish pores. Basal plate with four larger pores. Horn slender, conical, half as long as the shell. Feet eight, very slender, about three times as long as the shell, subvertical, with outer convex edge and convergent ends.

Petalospyris eupetala, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxii. fig. 4.

Shell nut-shaped, tuberculate, with slight sagittal stricture and scattered small circular pores. Basal plate with four large collar pores (sometimes surrounded by several small peripheral pores). Apical horn slender, conical, as long as the shell. Feet sixteen to twenty, laminated and truncate, of the same length, nearly vertical and parallel.

Shell nut-shaped, spinulate, with deep sagittal stricture and irregular, roundish pores. Basal plate with four large pores of equal size. Apical horn conical, twice as long as the shell. Feet twenty to thirty, laminated and truncate, as long as the shell, divergent.

Shell subspherical, with slight sagittal stricture and few small pores; on each side of the stricture four larger, square, annular pores. Basal plate with four large collar pores (two larger cardinal and two smaller jugular pores). Horn and feet conical, about half as long as the shell. Feet twenty to twenty-five, slightly curved, convergent.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms; also fossil in Barbados.

Subgenus 4. Petalospyromma, Haeckel.

Definition.—Basal plate with numerous (six or more) collar pores, commonly three or four larger central, and six to twelve smaller peripheral pores.

Shell nut-shaped, tuberculate, with slight sagittal stricture and irregular, roundish pores. Basal plate with nine pores (three large primary and three alternate pairs of small secondary pores). Nine long corresponding feet, twice to four times as long as the shell (three very thick primary, and three alternate pairs of thin secondary feet). All feet cylindrical, curved, widely divergent. Horn conical.

Petalospyris argiscus, Ehrenberg, 1875, Abhandl. d. k. Akad. Wiss. Berlin, p. 80, Taf. xxii. figs. 1, 2.

Petalospyris argiscus, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 539, Taf. xxxii. fig. 17, a, b.

Shell nut-shaped, tuberculate, with slight sagittal stricture and irregular, roundish pores. Basal plate with nine pores (three larger central and three alternate pairs of smaller peripheral pores). {1063}Apical horn slender, spindle-shaped, about as long as the shell. Twenty to twenty-five feet, of the same length, broad, lamellar and truncate, nearly vertical, slightly divergent.

Shell nearly cubical, papillate, without external sagittal stricture, with small, irregular, roundish pores. Basal plate with six pores (three larger and three alternate smaller). Apical horn conical, half as long as the shell. Feet twenty to thirty, one-half to one-third as long, conical, divergent.

Shell nearly cubical, smooth, without external stricture, but with a complete, parietal, square, sagittal ring. On each side of the ring four pairs of larger pores, whilst the lateral pores are smaller and more numerous. Basal plate also with four pairs of larger pores and smaller lateral pores. Apical horn and basal feet short, pyramidal, scarcely one-fourth as long as the shell. The three primary feet are larger than the six to nine secondary feet.

Shell nut-shaped, tuberculate, with slight sagittal stricture and irregular, roundish pores. Basal plate with twelve pores (four central larger and eight peripheral smaller pores). Apical horn slender, conical, about as long as the shell (sometimes ramified at the distal end). Feet sixteen to twenty, broadly lamellar, truncate, divergent, about as long as the shell.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms; also fossil in Barbados.

Shell nut-shaped, mammillate, without external stricture, but with complete external sagittal ring. Pores subregular, circular. Basal plate with four large central pores, surrounded by a circle of twelve to twenty small peripheral pores. Apical horn very large, spindle-shaped, one and a half times as long as the shell. Feet twenty-five to thirty, broadly lamellar, truncate, divergent, about as long as the shell.

Shell nut-shaped, smooth, with sharp sagittal stricture. Pores numerous, small, and circular; no larger annular pores. Basal plate with four larger and four alternate pairs of smaller pores. Horn conical, about as long as the shell. Feet fifteen to twenty, broadly lamellar, about twice as long as the shell, in the distal half forked.

Shell subspherical, smooth, with slight sagittal stricture. Pores small, roundish; on each side of the ring two pairs of larger annular pores. Basal plate with four pores. Horn stout, three-sided prismatic, half as long as the shell. Feet twelve to sixteen, lamellar, lobate (the most part with three lobes), nearly vertical, about as long as the shell.

Genus 464. Anthospyris,^[82] Haeckel, 1881, Prodromus, p. 443.

Definition.—Zygospyrida with numerous (seven to nine or more) basal feet and three coryphal horns.

The genus Anthospyris differs from the preceding Petalospyris, its ancestral form, in the possession of three horns on the coryphal face (one odd middle apical horn and two paired frontal horns, one on each side). The former therefore bears to the latter the same relation that Triceraspyris does to Tripospyris and Liriospyris to Hexaspyris.

Shell nut-shaped, mammillate, with deep sagittal stricture and irregular, polygonal pores. Basal plate with two large ovate pores (?). The pediculate apical horn and the two frontal horns stout and short, conical, twice to three times as large as the conical papillæ of the surface. Feet twelve to fifteen, lanceolate lamellar, pointed, divergent, about as long as the shell.

Shell subspherical, thorny, with slight sagittal stricture and irregular, roundish pores. Basal plate with three large pores. The three horns spindle-shaped, half as long as the ten to twelve thin feet, which are pediculate, shovel-shaped, a little divergent, and shorter than the shell.

Petalospyris diaboliscus, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 12; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 80, Taf. xxii. fig. 3.

Shell nut-shaped, smooth, with slight sagittal stricture and small circular pores. Basal plate with four large pores. Apical horn straight conical, frontal horns curved laterally. Feet nine to twelve, of about the same length as the horns and the shell, broad lamelliform, truncate, nearly vertical, slightly curved.

Petalospyris arachnoides, Haeckel, 1862, Monogr. d. Radiol., p. 294, Taf. xii. fig. 7.

Shell nut-shaped, tuberculate, with slight sagittal stricture and irregular, polygonal pores. Basal plate with four large pores (?). Apical horn straight, conical, longer than the two curved lateral horns. Feet ten, slender, S-shaped, widely divergent, about as long as the shell is broad.

Dimensions.—Shell 0.05 long, 0.08 broad; horns 0.03 to 0.05 long, feet 0.08 long.

Shell campanulate, spiny, with deep sagittal stricture and irregular, roundish pores. On each side of the stricture three pairs of larger annular pores. Basal plate with two large square pores. The three horns of the same size as, and similar form to, the ten to fifteen feet, slender pyramidal, straight, divergent, about half as long as the shell. (This species is very variable and closely allied to Ceratospyris.)

Shell nut-shaped, spiny, with a deep sagittal stricture and small circular pores. On each side of the stricture two pairs of very large square annular pores. Basal plate with four larger collar {1066}pores and a corona of numerous small peripheral pores. Three horns spindle-shaped, divergent, about half as long as the shell. Feet twenty-five to thirty, broad, lamellar, lanceolate, pointed, divergent, nearly as long as the shell.

Shell nut-shaped, tuberculate, with distinct sagittal stricture and small regular circular pores. Basal plate with numerous small pores. Apical horn very large, spindle-shaped, twice as long as the shell; frontal horns small, scarcely one-fourth as long, curved laterally. Feet twenty-five to thirty, three to four times as long as the shell, lamellar, lanceolate, pointed, parallel, vertical.

Genus 465. Ceratospyris,^[83] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Zygospyrida with numerous (seven to twelve or more) basal feet and numerous coryphal horns.

The genus Ceratospyris differs from all the other Zygospyrida in the possession of numerous large spines on the surface of the shell, which usually exhibits only a small number of large pores or meshes. The lower spines which cover the inferior or basal face of the shell (usually nine to twelve or more) may be compared to the descending "basal feet" of the other Zygospyrida; the upper spines, however, which cover the superior or coryphal face (usually six to nine, rarely more), may be regarded as "coryphal horns." In many species of this genus the lattice-work of the shell is of a peculiar loose kind, with few large meshes, resembling the wicker-work of the Plectanida.

Subgenus 1. Lophospyris, Haeckel, 1881, Prodromus, p. 443.

Definition.—Spines simple, not branched. Meshes of the shell usually polygonal, or roundish with polygonal frames. Bars of the network prismatic.

Shell polyhedral, with deep sagittal stricture, studded with twenty-four to thirty long simple straight slender pyramidal spines, which are as long as the shell or longer. All pores large, polygonal. On the frontal and the occipital face two pairs of very large pores only, the superior {1067}pentagonal, larger than the inferior tetragonal. Basal plate with two triangular pores. Bars of the loose framework three-sided prismatic, thin.

Ceratospyris pentagona, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 287, Taf. x. fig. 15.

Shell polyhedral, with slight sagittal stricture, studded with twenty-four to thirty small simple conical spines, which are shorter than one-fourth of the shell. Most pores pentagonal. On the frontal and the occipital face two pairs of large pores only, the superior smaller than the inferior. Basal plate with four quadrangular pores. Bars of the network prismatic, thin.

Shell polyhedral, with slight sagittal stricture, studded with thirty to forty prismatic spines which are not longer than half the shell. Most pores pentagonal. On the frontal face two, on the occipital three pairs of larger pores; the inferior the largest. Basal plate with two rhomboidal pores (?). Bars of the network three-sided prismatic, thin. Dedicated to my dear friend, the excellent poet and naturalist, Hermann Allmers, of Rechtenfleth.

Shell polyhedral, with deep sagittal stricture, studded with fifty to seventy prismatic spines; two inferior (pectoral) spines about as long as the shell, the others much shorter. Pores polygonal. On the frontal and the occipital face one pair of very large pores. Basal plate with two distinctly hexagonal pores. Bars of the loose network prismatic. Dedicated to my dear friend, the excellent author and painter, Ludwig Mulder, of the Hague.

Shell polyhedral, with slight sagittal stricture, studded with thirty to forty prismatic spines, which are about half as long as the shell (two or four inferior are longer). Pores roundish, with polygonal frames. On the frontal and occipital face two pairs of larger pores (the superior {1068}smaller). Basal plate with two large pentagonal pores. Bars of the network prismatic. Dedicated to my dear friend, the celebrated botanist, Professor Eduard Strasburger, of Bonn.

Ceratospyris mülleri, Stöhr, 1880, Palæontogr., vol. xxvi. Taf. iii. fig. 15.

Shell polyhedral, with slight collar stricture, studded with forty to fifty pyramidal spines, shorter than half the shell. Pores circular, with pentagonal frames of the same breadth, all nearly of equal size. (Basal plate with four pores?) Bars of the network prismatic. Dedicated to Johannes Müller.

Shell nut-shaped, with deep sagittal stricture, studded with forty to fifty strong conical spines; six basal spines as long as the shell and two to three times as long as the others. Pores roundish polygonal, twice to three times as broad as the bars; two pairs of larger pores on each side of the ring. (Basal plate with four large pores?) Bars of the network rounded, thick. Dedicated to my dear friend, the excellent author, Ernst Krause (Carus Sterne), of Berlin.

Habitat.—Western Tropical Pacific (Philippine Sea), Station 206, depth 2100 fathoms.

Shell nut-shaped, with slight sagittal stricture, studded with ten to twelve longer club-shaped spines (about as long as the shell) and numerous smaller conical spines. Pores irregular, roundish, numerous; two pairs of larger pores on each side of the ring. Basal plate with four large pores. Bars of the network rounded. Dedicated to my honoured friend and colleague, the celebrated investigator of psychical ontogeny, Professor William Preyer, of Jena.

Ceratospyris echinus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx, fig. 12.

Shell subspherical, with slight sagittal stricture, studded with numerous conical curved spines; six basal and one apical spine are larger than the others, about as long as the shell. Pores numerous, small, circular. Basal plate with numerous pores. Bars of the network roundish.

Subgenus 2. Cladospyris, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Ceratospyris ramosa, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 7.

Cladospyris ramosa, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Shell nut-shaped, with slight sagittal stricture, studded with numerous conical, irregularly branched spines. The largest about as long as the shell. Pores irregular, roundish; on each side of the ring two pairs of larger pores. Basal plate with four pores. Bars of the network roundish.

Shell nut-shaped, with sharp sagittal stricture, studded with numerous pyramidal spines; two basal spines are larger, as long as the shell, and irregularly branched. Pores polygonal; on each side of the ring three pairs of larger pores. Basal plate with four large pores. Dedicated to my dear friend, the excellent monistic philosopher, B. von Carneri.

Shell nut-shaped, with deep sagittal stricture, studded with numerous conical strong spines, about one-fourth as long as the shell. Basal spines irregularly branched, with root-like ends. Pores irregular, roundish, some larger pores on each side of the ring. Basal plate with four larger pores. Bars of the network roundish.

Genus 466. Gorgospyris,^[84] Haeckel, 1881, Prodromus, p. 443.

Definition.—Zygospyrida with numerous (seven to twelve or more) basal feet, without coryphal horns.

The genus Gorgospyris agrees with the three preceding genera in the possession of numerous basal feet, but differs from them in the complete absence of any horns on the coryphal face. It represents therefore the "hornless polypedal Zygospyrida," and may {1070}be derived from Petalospyris by loss of the original apical horn. The feet are commonly numerous, and often form a circle around the margin of the basal plate, similar to the circle of tentacles in many Medusæ (Gorgon).

Subgenus 1. Gorgospyrium, Haeckel.

Shell hemispherical, papillate, with slight sagittal stricture and subregular circular pores. Basal plate with three large collar pores (by mistake not correctly represented in the figure). Ten to twelve slender feet, twice as long as the shell, strongly curved and divergent, of equal length.

Shell misshaped, smooth, with deep sagittal stricture and irregular, roundish pores. Basal plate with three large collar pores, alternating with three pairs of smaller pores. Sixteen to twenty slender feet, about as long as the shell, slightly curved and divergent, of nearly equal length.

Petalospyris pentas, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxii. fig. 11.

Shell nut-shaped, smooth, with slight sagittal stricture and unequal circular pores. Basal plate with three large central pores, alternating with three pairs of smaller pores, and with a peripheral circle of smaller pores. Twenty-four to thirty short truncated feet, shorter than half the shell.

Shell hemispherical, papillate, with slight sagittal stricture and subregular circular pores. Basal plate with four larger and four alternating smaller pores. Feet sixteen to twenty, slender, carved, divergent; four primary feet larger, twice to three times as long as the shell and the other feet.

Shell nut-shaped, rough, with deep sagittal stricture and irregular, roundish pores; two to three pairs of larger annular pores on each side of the stricture. Basal plate with four large collar pores. Feet eight, short, triangular, vertical, about one-fourth as long as the shell.

Shell nut-shaped, thorny, with sharp sagittal stricture and irregular, roundish pores. Two pairs of larger annular pores on each side of the ring. Basal plate with two very large circular pores only. Eight to ten short feet vertical, about one-fourth as long as the shell, with an elegant papillate knob at the distal end.

Shell nut-shaped, tuberculate, with subregular circular pores. Basal plate with four larger and four alternate pairs of smaller pores. Feet fifteen to twenty-five, broad, lamellar, vertical, truncate, about as long as the shell, of irregular size and form, very variable.

Subgenus 2. Thamnospyris, Haeckel, 1881, Prodromus, p. 443.

Shell hemispherical, smooth, with slight sagittal stricture and small regular, circular pores. Basal plate with four large central and a circle of small pores. Feet fifteen to twenty, broad, lamellar, confluent at the base, about as long as the shell, irregularly divided or forked.

Thamnospyris thamnopodia, Haeckel, 1881, Prodromus, p. 143.

Shell nut-shaped, tuberculate, with deep sagittal stricture and irregular, roundish pores. Basal plate with numerous small pores. Feet twenty to thirty, slender, curved, divergent, twice to three times as long as the shell, irregularly branched.

Subfamily 8. Circospyrida, Haeckel, 1881, Prodromus, p. 443.

Genus 467. Circospyris,^[85] Haeckel, 1881, Prodromus, p. 444.

The genus Circospyris and the following closely allied genus Dictyospyris represent together the small subfamily Circospyrida, differing from all other Zygospyrida in the absence of feet on the basal face. They have probably arisen from the Tripospyrida (Tripospyris) by reduction and loss of the feet (in the same way as the eradiate Cyrtoidea from the triradiate). But it is also possible that many of the Circospyrida (if not all) are derived directly from the Semantida (Clathrocircus) by the closing of the two lateral openings and by completing the framework.

Shell nut-shaped, compressed, smooth, with prominent sagittal ring. On each side of the ring three to four pairs of very large annular polygonal pores. Lateral pores small and numerous, roundish. Basal plate with two large pores only. Horn slender, conical, shorter than half the shell.

Dictyospyris gigas, Ehrenberg, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. xix. fig. 6.

Shell nut-shaped, tuberculate, with distinct sagittal stricture. On each side of the ring four pairs of larger annular pores. Lateral pores roundish, smaller. Basal plate with four large central and a circle of eight to twelve smaller peripheral pores. Horn cylindrical, about half as long as the shell (in the inverted figure of Ehrenberg directed downwards).

Dimensions.—Shell 0.1 to 0.15 long, 0.15 to 0.2 broad; horn 0.05 to 0.08 long.

Dictyospyris tridentata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 70, Taf. xix. fig. 10, a, b.

Shell nut-shaped, smooth, with sharp sagittal stricture. On each side of the ring two pairs of large annular pores. Lateral pores roundish, smaller. Basal plate with six large pores. Horn slender, cylindrical, about as long as the shell, with three sharp teeth at the distal end.

Genus 468. Dictyospyris,^[86] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

The genus Dictyospyris, the last and simplest of the twenty-eight genera of Zygocyrtida, may be regarded either as a primordial ancestral form of this large family, or more probably as the last and most reduced form of it. In the former case the total absence of coryphal horns and basal feet is primary, in the latter case secondary, effected by phylogenetic reduction and loss. But it is also possible that in one part of the numerous species of this genus the former case, and in another the latter takes place, and that one part of Dictyospyris may be directly developed from the Semantida or Coronida (the lattice shell becoming complete), another part arising from the Tripospyrida or Dipospyrida (the horns and feet becoming lost).

Subgenus 1. Dictyospyrantha, Haeckel.

Definition.—Basal plate with two large pores only (the primary jugular pores of Semantis).

Shell nut-shaped, smooth, or somewhat tuberculate, with deep sagittal stricture. Pores not numerous, large, roundish-polygonal; three pairs of large annular pores on each side of the ring. Basal plate with two very large pentagonal roundish collar pores.

Shell nut-shaped, covered with irregular ramified tubercles (like stalactites), with deep sagittal stricture. Pores not numerous, large, irregular, roundish. Two pairs of large triangular pores on each side of the ring (the inferior larger). Basal plate with two very large semicircular collar pores.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms; also fossil in Barbados.

Shell subspherical, tuberculate, with slight sagittal stricture. Pores very numerous, small, circular. No larger pores on either side of the ring. Basal plate with two very large circular pores, surrounded by a circle of smaller pores.

Subgenus 2. Dictyospyrella, Haeckel.

Definition.—Basal plate with three large collar pores (two paired posterior cardinal pores and an odd anterior sternal pore).

Shell nut-shaped, smooth, with deep sagittal stricture. Pores not numerous, large, polygonal roundish, two pairs of very large annular pores on each side of the ring. Basal plate with three large triangular pores. No free internal procolumella.

Dictyospyris tristoma, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 70, Taf. xix. fig. 9.

Shell nut-shaped, tuberculate, with slight sagittal stricture. Pores numerous, irregular, roundish. Three pairs of larger annular pores on each side of the ring. Basal plate with three large semi-circular pores (the sternal odd pore apparently halved by an internal free procolumella).

Dictyospyris triloba, Ehrenberg, 1876, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 70, Taf. xix. fig. 8.

Shell nut-shaped, spinulate, without external stricture, but with a complete internal sagittal ring. Pores numerous, subregular circular; no larger annular pores. Basal plate with three large, heart-shaped two-lobed collar pores.

Dictyospyris gigas, Bütschli, 1880, Zeitschr. f. wiss. Zool., vol. xxxvi., p. 539, Taf. xxxii. fig. 14a, 14b.

Shell subspherical, smooth, with a half (ventral) sagittal stricture, and a nearly complete internal ring. Pores very numerous and small, circular. No larger annular pores. Basal plate with three large collar pores (the sternal odd pore apparently divided into two jugular pores by the visible free procolumella.) (Compare Circospyris gigas, p. 1072 = Dictyospyris gigas, Ehrenberg).

Subgenus 3. Dictyospyrissa, Haeckel.

Definition.—Basal plate with four large collar pores (two larger posterior cardinal and two smaller anterior jugular pores).

Dictyospyris fenestra, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. xix. fig. 11.

Shell nearly cubical, smooth, without external sagittal stricture. Internal sagittal ring complete. Pores small, roundish; on each side of the ring two crossed pairs of large, square, equal, annular pores. Basal plate also with four longer pores of nearly equal size.

Dictyospyris tetrastoma, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 70, Taf. xix. fig. 12.

Shell nut-shaped, tuberculate, with slight sagittal stricture. Pores numerous, irregular, roundish. No larger annular pores. Basal plate with four large ovate collar pores (the two cardinal twice as large as the two jugular pores).

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific; also fossil in Barbados and Sicily.

Dictyospyris spinulosa, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 70, Taf. xix. fig. 13.

? Ceratospyris borealis, Bailey, 1856, Amer. Journ. of Science and Arts, vol. xxii. pl. i. fig. 3.

Shell nut-shaped, spinulate, without external stricture, with an internal free sagittal ring. Pores numerous, irregular, roundish; on each side of the ring two pairs of very large square pores. Basal plate with four large collar pores.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms; also fossil in Barbados.

Shell mammillate, nut-shaped, with deep sagittal stricture. Mammillæ of the surface hemispherical, with a conical apex. Pores not numerous, large, roundish. Two pairs of large pores on each side of the ring. Basal plate with four large pores.

Shell tuberculate, nut-shaped, nearly cubical, without external sagittal strictures. Pores not numerous, large, polygonally roundish. Bars between them compressed, elevated, with large, campanulate or flower-like tubercles on the nodal points. Basal plate with four large pores.

Shell nut-shaped, smooth, with deep sagittal stricture. Pores numerous, small, circular, on each side of the ring three to four times as large as on the lateral sides. Basal plate with four very large collar pores and a circle of twenty to twenty-five very small peripheral pores.

Dictyospyris messanensis, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 46, Taf. ii. fig. 8.

Dictyospyris messanensis, Haeckel, 1862, Monogr. d. Radiol., p. 291.

Shell nut-shaped, spinulate, with deep sagittal stricture. Pores numerous and small, irregular roundish. No larger annular pores on the sides of the ring. Basal plate with four large, nearly equal, pear-shaped collar pores.

Subgenus 4. Dictyospyromma, Haeckel.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores small, irregular, roundish. Three pairs of larger pores on each side of the ring. Basal plate with six large pores; the middle pair (cardinal) twice as large as the anterior (jugular) and the posterior (cervical).

Shell ellipsoidal, smooth, without external sagittal stricture, but with an internal free sagittal ring. Pores small and numerous, regular, circular. No larger annular pores. Basal plate with nine pores, three larger interradial alternating with three pairs of adradial.

Shell nut-shaped, mammillate, with distinct sagittal stricture. Pores small and numerous, irregular, on each side of the ring three to five times as large as on the lateral sides. Basal plate with twelve large pores (four central and four alternate pairs of peripheral).

Family LIII. Tholospyrida, n. fam.

Definition.—Spyroidea with a galea, but without thorax; the shell being composed of the bilocular cephalis and of an aboral cupola or galea arising from its coryphal face.

The family Tholospyrida differs from the preceding Zygospyrida, its ancestral group, in the development of a galea, i.e., a fenestrated hemispherical or dome-shaped cupola, which covers the upper face of the cephalis like a cap.

Only three species of this family have been hitherto described: Pylospyris (or Spyridobotrys) trinacria, figured in my Monograph (1862), Pylospyris (or Lithopera) denticulata, figured by Ehrenberg (1872), and Lophospyris (or Ceratospyris) acuminata, figured by Hertwig (1879). Fourteen new species have been found in the collection of the Challenger, which we dispose here among five genera. These may be derived from corresponding genera of Zygospyrida by the development of a galea.

The number and disposition of the terminal feet around the basal plate do not vary so much in the Tholospyrida as in the Zygospyrida. We find here only one genus with three feet, Tholospyris (corresponding to Tripospyris); one genus with two lateral feet, Lophospyris (corresponding to Dipospyris); and two genera with numerous feet, the horned Sepalospyris and the hornless Tiarospyris (the former corresponding to Petalospyris, the latter to Gorgospyris). The fifth genus (Pylospyris) has no feet at all, and may be derived from Circospyris among the Zygospyrida.

The cephalis exhibits in the Tholospyrida the same typical structure which we have described above of all Spyroidea (compare p. 1017). The cupola or galea, arising from its upper face, seems to be a secondary production, perhaps caused by an apical growth of the central capsule, or in other cases by descending branches of the apical horn, which cover the apical face of the calymma with protecting network.

Synopsis of the Genera of Tholospyrida.

Genus 469. Tholospyris,^[87] Haeckel, 1881, Prodromus, p. 441.

The genus Tholospyris is probably the common ancestral form of the Tholospyrida, and has arisen from Tripospyris by development of a galea or cupola; this is composed of the apical horn, the lateral branches of which become connected with lateral spines arising from the coryphal face of the cephalis, and of lattice-work developed between the former and the latter. The three descending feet of the basal face are the typical cortinar feet (one odd caudal and two paired pectoral), the same as in the old ancestral genera Cortina, Plagoniscus, Tripospyris, &c.

Subgenus 1. Tholospyrium, Haeckel.

Shell campanulate, smooth, as broad as long, with deep sagittal stricture. Cephalis compressed, with irregular roundish pores; two or three pairs of larger annular pores on each side of the ring. Basal plate with four large pores. Galea with two very large opposite holes (an occipital and a frontal opening). A slender free perpendicular columella connects the uppermost part of the sagittal ring with the strong three-sided pyramidal apical horn. All three feet of equal length, half as long as the ring, three-sided, prismatic, divergent, with three dentated edges.

Shell roundish polyhedral, smooth, with slight sagittal stricture. Cephalis nearly cubical, with irregularly roundish pores; two or three pairs of larger pores on each side of the ring. Basal plate with two very large pores. Galea pyramidal, with two large occipital holes. Columella enclosed in the dorsal wall of the galea, prolonged into an oblique pyramidal spine of the same length. Two pectoral feet pyramidal, nearly vertical and as long as the ring, twice as long as the caudal foot.

Shell helmet-shaped, thorny, with deep sagittal stricture. Cephalis campanulate, with subregular circular pores. Basal plate with three large pores. Galea hemispherical, separated from the cephalis by a sharp horizontal stricture; pores smaller. A slender free columella connects the apex of the ring with the strong conical apical horn, which is half as long as the ring. All three feet of equal length, divergent conical, as long as the horn.

Subgenus 2. Tholospyridium, Haeckel.

Shell helmet-shaped, smooth, with deep sagittal stricture. Cephalis nearly spherical, with irregularly polygonal pores; four or five pairs of larger annular pores on each side of the strong angular ring. Cupola flat, conical, with two pairs of larger pores. Columella enclosed in its dorsal wall, {1080}bearing an irregularly branched horn. Caudal foot short conical, simple. Two pectoral feet half as long as the shell, angular, subvertical, irregularly branched.

Shell pear-shaped or cupola-shaped, smooth, with slight sagittal stricture. Cephalis not distinctly separated from the galea, as the ring in the uppermost part of the shell-wall becomes obliterated. Pores irregularly polygonal, small and numerous. Basal plate with four large pores. Apical horn and the three divergent feet, irregularly branched; feet nearly as long as the shell, about four times as long as the horn.

Genus 470. Lophospyris,^[88] Haeckel, 1881, Prodromus, p. 443 (sensu emendato).

The genus Lophospyris differs from the preceding Tholospyris, its probable ancestral form, in the absence of the caudal foot, and therefore bears to it the same relation that Dipospyris does to Tripospyris. The two pectoral feet are alone developed and are placed opposite in the frontal plane. Lophospyris may also be derived from Dipospyris by the formation of a galea.

Shell ovate, spinulate, with sharp transverse coronal constriction. Cupola hemispherical, half as large as the nut-shaped cephalis. Pores irregularly roundish, much larger on the sagittal constriction. Apical horn pyramidal, about half as long as the shell. Two lateral feet cylindrical, strongly curved, about as long as the shell, with some irregular branches; together forming a nearly complete circle.

Ceratospyris acuminata, R. Hertwig, 1879, Organism. d. Radiol., p. 70, Taf. vii. fig. 2.

Shell campanulate, smooth, without external transverse stricture. Cupola conical, half as long and broad as the nut-shaped cephalis. Pores irregularly roundish, on each side of the sagittal {1081}strictures much larger. Basal plate with four large triangular pores. Apical horn slender, prismatic; its outer free part of the same length as the inner columella, and as the two lateral feet, which are curved, shorter than half the ring.

Dimensions.—Shell 0.08 long, 0.09 broad; ring 0.06 long; horn and feet 0.03 long.

Shell ovate, spiny, with deep transverse stricture. Cupola large, campanulate, nearly as long and two-thirds as broad as the nut-shaped cephalis. Pores irregular, roundish, of little different size, Basal plate with numerous (eight to twelve) similar pores. Apical horn large, nearly as long as the shell, surrounded by a bunch of smaller divergent spines. Two lateral feet divergent, larger than the shell, cylindrical; at the distal end irregularly branched, at the base surrounded by some smaller spines.

Genus 471. Sepalospyris,^[89] Haeckel, 1881, Prodromus, p. 443.

Definition.—Tholospyrida with numerous basal feet (eight to twelve or more). Galea with a horn.

The genus Sepalospyris has been derived from the similar Petalospyris by development of a galea or cupola on the coryphal face of the cephalis, or from Tholospyris by multiplication of the basal feet. The latter (in the two observed species from twelve to twenty-five) form a regular corona around the basal plate.

Shell ovate, rough, with sharp transverse stricture. Cupola with delicate network, hemispherical, about two-thirds as long and broad as the nut-shaped thorax. Pores of the latter irregular, roundish; two or three pairs of large pores on each side of the sagittal stricture. Apical horn conical, half as long as the shell. Basal coronet with twelve to fifteen broad, lamellar, truncate, vertical feet, somewhat shorter than the cephalis.

Dimensions.—Shell 0.12 long, 0.13 broad; ring 0.06 long; horn 0.04; feet 0.05 long.

Shell campanulate, rough, with deep transverse stricture. Cupola hemispherical, about one-third as long and broad as the nut-shaped thorax. Pores irregular, roundish, a little different in {1082}size. Apical horn pyramidal, about as long an the shell. Basal coronet with twenty to twenty-five slender, lamellar, pointed, vertical feet, longer than the shell.

Dimensions.—Shell 0.11 long, 0.12 broad; ring 0.07 long; horn 0.1; feet 0.12 to 0.18 long.

Genus 472. Tiarospyris,^[90] Haeckel, 1881, Prodromus, p. 443.

Definition.—Tholospyrida with numerous basal feet (eight to twelve or more). Galea without a horn.

The genus Tiarospyris has probably been derived from the preceding Sepalospyris by reduction and loss of the free apical horn; it therefore bears to it the same relation that the similar Gorgospyris does to Petalospyris.

Shell nut-shaped, smooth, with deep sagittal stricture. Cephalis on the lateral sides with numerous small roundish pores, on each side of the ring with a pair of very large holes. Basal plate with two large collar pores. Cupola flat, cap-shaped, with two large parietal pores above the ring. Coronet with eight conical, slightly divergent feet, about one-fourth as long as the shell.

Shell helmet-shaped, with deep sagittal stricture. Cephalis with irregular, polygonal pores; on each side of the ring two pairs of larger annular pores. Basal plate with four large pores. Cupola high, conical, nearly as long as the cephalis, separated from it by a distinct coronal stricture. Basal coronet with twelve to sixteen slender curved divergent feet, nearly as long as the shell.

Shell subspherical, smooth. Cephalis on the lateral sides with small roundish, double-contoured pores, on each side of the ring with three to five pairs of larger pores, each of which is closed by a thin fenestrated lamella (different on the frontal face, fig. 9, and the dorsal face, fig. 10). Cupola flat, cap-shaped, separated by a distinct coronal stricture, with similar pores. Basal coronet with, ten to twelve short conical convergent feet.

Shell amphora-shaped, in the upper half smooth, in the lower spiny, without external sagittal stricture. Cephalis subspherical with a small number of irregular, large, roundish pores, which are closed by a thin fenestrated lamella. Cupola flat, cap-shaped, with numerous small pores. Base covered with numerous conical divergent feet of different sizes, the largest one-third as long as the shell. Internal sagittal ring ovate, nearly free.

Genus 473. Pylospyris,^[91] Haeckel, 1881 Prodromus, p. 443.

The genus Pylospyris was first known from a Mediterranean species, called by me, in 1862, Spyridobotrys trinacria. As this name was given erroneously, on the supposition of a near relation to the Botryodea (= Polycyrtida), I changed it afterwards to Pylospyris. This genus differs from the other Tholospyrida in the total absence of basal feet, and may therefore be derived either from them by reduction of the feet, or from Dictyospyris by formation of a galea.

Lithopera denticulata, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. xii. II. fig. 7.

Lithobotrys denticulata, Ehrenberg, 1844, Monatsber. d. Akad. Berlin, p. 203.

Shell spinulate, with slight coronal and deep sagittal constriction, with irregular, roundish pores of variable size. Galea hemispherical, about half as long and broad as the nut-shaped cephalis. No symmetrically disposed larger pores.

Spyridobotrys trinacria, Haeckel, 1862, Monogr. d. Radiol., p. 341, Taf. xii. figs. 8, 9.

Shell tuberculate, with sharp coronal and sagittal stricture. Galea campanulate, with very small circular pores, and a short conical apical horn of the same length. Cephalis nut-shaped, with large, irregular, roundish pores; two pairs of larger annular pores on each side of the sagittal ring, also four larger pores in the basal plate.

Shell rough, with deep coronal and slight sagittal constriction. Galea hemispherical, with numerous small irregular, roundish pores, about half as long as the cephalis, with a slender conical horn of twice the length. Cephalis nut-shaped, with larger roundish pores of very unequal size, three pairs of larger pores on each side of the ring. Basal plate with two larger pores.

Family LIV. Phormospyrida, Haeckel (sensu emendato) (Pl. 83, figs. 13-15; Pl. 95, figs. 17-19).

Phormospyrida, Haeckel, 1881, Prodromus, p. 442.

Definition.—Spyroidea with a thorax, without galea; the shell composed of the bilocular cephalis and of a simple thorax arising from its basal face.

The family Phormospyrida differs from the Zygospyrida, their ancestral group, in the development of a thorax, or a second fenestrated shell-joint, which arises from the lower face of the cephalis. It corresponds, therefore, to the Dicyrtida among the Cyrtoidea, and may perhaps be, wholly or partially, the ancestral group of the latter. When the sagittal ring and the longitudinal constriction of the cephalis disappear, the Phormospyrida pass over into the Dicyrtida.

Only three species of this family have been hitherto known, which were found fossil in Barbados, and described by Ehrenberg (1875) as Lithobotrys stiligera and Petalospyris confluens, and by Bütschli (1882) as Petalospyris anthocyrtoides. Fifteen other species are found in the Challenger collection, which we dispose here among five genera.

Two of these five genera (the horned Acrospyris and the hornless Phormospyris) possess the three typical basal feet of Cortina and Tripospyris, and may be derived from these genera by the development of network between the bases of the feet. The three other genera possess numerous feet, and may be derived in the same way from the Polyspyrida; the apical face differs in the three genera, in Desmospyris it is hornless, in Patagospyris it bears an apical horn, and in Rhodospyris three horns (an apical and two lateral or frontal).

The cephalis in the Phormospyrida exhibits the same typical structure, which we have described above, of all Spyroidea (compare, p. 1017). The thorax or the second joint of the shell arises by reticular connection of the bases of the basal feet, and represents a cylindrical or truncate-conical joint in the polypodal forms, or a three-sided joint in the tripodal forms. The terminal aperture or the mouth of the thorax is constantly open, and surrounded by the free ends of the feet.

Subfamily 1. Acrospyrida, Haeckel, 1881, Prodromus, p. 441 (sensu emendato).

Definition.—Phormospyrida with three basal feet (an odd caudal and two paired pectoral).

Genus 474. Acrospyris,^[92] Haeckel, 1881, Prodromus, p. 441.

The genus Acrospyris is probably the oldest and most primitive among the Phormospyrida, perhaps the original ancestral form of this family. It has been derived from Tripospyris by the development of lattice-work between the three basal feet, forming a second joint or thorax. It has also therefore a close relation to the simplest forms of the triradiate Dicyrtida: Dictyophimus, Clathrocanium, &c. It differs from these in the distinct sagittal constriction of the cephalis, which divides it into two lateral loculi.

Shell tuberculate, with distinct collar and deep sagittal stricture. Cephalis nut-shaped, with numerous irregular, roundish pores; three pairs of larger annular pores on each side of the ring. Basal plate with four larger pores (two major cardinal and two minor jugular pores). Apical horn slender, pyramidal, curved, about as long as the shell, with three recurved short spines. Thorax three-sided, about twice as large as the cephalis, with three large basal holes and a broad riband with numerous smaller holes; three ribs between them stout, pyramidal, strongly curved, prolonged into three convergent crescentic feet.

Shell smooth. Cephalis and thorax of nearly the same structure and form as in the preceding species; it differs from the latter in the shape of the three stout basal feet, which are {1086}straight, much longer than the thorax, divergent, and at the broader base irregularly fenestrated, without three larger holes.

Shell three-sided pyramidal, with slight collar stricture. Cephalis campanulate, with deep sagittal stricture and stout ring, armed with a strong pyramidal horn of the same length. Thorax shorter and broader, truncate. Pores irregular, roundish, scarce. Three feet divergent, three-sided pyramidal, as long as the cephalis.

Shell spinulate, with deep sagittal and very deep collar stricture. Cephalis very large, nut-shaped, twice as long and broad as the small, truncate, pyramidal thorax. Pores irregular, roundish. Horn spindle-shaped, nearly as long as the cephalis; the three divergent feet are of the same form and size as the horn, and arise as three ribs from the deep collar stricture.

Shell very thin-walled and fragile, with deep sagittal and collar strictures. Pores very small and numerous, circular. Cephalis nut-shaped, nearly spherical, with a slender bristle-shaped horn of the same length. Basal stricture with two large collar pores only (luminella). Thorax nearly three-sided prismatic, longer than the cephalis, with three parallel ribs, prolonged into three slender, long, bristle-shaped feet.

Genus 475. Phormospyris,^[93] Haeckel, 1881, Prodromus, p. 442 (sensu emendato).

The genus Phormospyris has been derived from Acrospyris, its ancestral form, by reduction and loss of the apical horn; it therefore bears to the latter the same relation that Tristylospyris has to the ancestral Tripospyris.

Cephalis nut-shaped, thorny, with deep sagittal and collar strictures, half as large as the pyramidal thorax. Mouth of the latter dilated and ciliated, twice as broad as the cephalis. Pores irregular, polygonal, with thin bars. Three cylindrical, straight, divergent ribs descend in the wall of the thorax, and are prolonged over the mouth into three short conical teeth.

Cephalis nut-shaped, with deep sagittal and collar strictures, about twice as large as the thorax. Mouth of the latter half as broad as the cephalis. Pores very small and numerous, subregular, circular. Collar plate with four large triangular pores. In the wall of the thorax three vertical prismatic ribs descend, which are prolonged over the mouth into three parallel feet of the same length.

Cephalis nut-shaped, with deep sagittal and collar strictures, smaller than the thorax. Mouth of the latter nearly as broad as the cephalis. Pores circular, double-contoured, larger in the thorax than in the cephalis. The thorax has no lateral ribs, but bears around the mouth three large triangular lamellar terminal feet.

Subfamily 2. Rhodospyrida, Haeckel.

Definition.—Phormospyrida with a corona of numerous (nine to twelve or more) basal feet.

Genus 476. Patagospyris,^[94] Haeckel, 1881, Prodromus, p. 443.

Definition.—Phormospyrida with numerous basal feet (nine to twelve or more) and an apical horn.

The genus Patagospyris and the two following closely allied genera differ from the two preceding tripodal genera in the multiplication of the basal feet, and therefore have to the latter the same relation that the Polyspyrida (Petalospyris) bear to the Tripospyrida (Tripospyris). When the numerous basal feet of Petalospyris become connected by lattice-work, Patagospyris arises.

Petalospyris confluens, Ehrenberg, 1885, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxii. fig. 5.

Shell tuberculate, with distinct sagittal and collar strictures. Pores irregular, roundish. Cephalis nut-shaped, larger than the short truncate thorax. Horn conical, shorter than the cephalis. Peristome with a coronet of twelve to fifteen short triangular feet, which are parallel and vertical, slightly curved and shorter than the thorax.

Shell tuberculate, with slight sagittal and sharp collar strictures. Pores subregular, circular. Cephalis subspherical, about as large as the truncate subcylindrical thorax. Horn spindle-shaped, about as long as the cephalis. Peristome with a coronet of fifteen to twenty divergent lanceolate lamellar feet, longer than the thorax.

Lithobotrys stiligera, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. iii. fig. 17.

Shell smooth, hyaline, with deep sagittal and collar strictures. Pores very small and few. Cephalis nut-shaped, bilobed, of the same breadth as the cylindrical thorax. Horn conical, about as long as the cephalis. Peristome with a coronet of six to nine broad lamellar feet (in Ehrenberg's figure broken off).

Shell smooth, with deep sagittal and deep collar strictures. Pores irregular, roundish, of various sizes, numerous. Cephalis nut-shaped, with two inflated bosoms, about twice as broad as the short cylindrical thorax. Horn stout, pyramidal, about as long as the cephalis. Peristome with a coronet of fifteen to twenty parallel and vertical triangular lamellar feet, nearly as long as the thorax.

Genus 477. Rhodospyris,^[95] Haeckel, 1881, Prodromus, p. 443.

Definition.—Phormospyrida with numerous basal feet (nine to twelve or more), and with three coryphal horns.

The genus Rhodospyris differs from the preceding Patagospyris in the development of three coryphal horns (one odd middle apical horn, and two paired frontal horns on each of its sides), and therefore bears the same relation to the latter that the similar Anthospyris does to Petalospyris. When the numerous basal feet of Anthospyris become connected by lattice-work, Rhodospyris arises.

Cephalis nut-shaped, with deep sagittal stricture, and three short apical horns of half its length; the middle odd horn is straight, the two paired lateral horns are curved outwards. Thorax somewhat larger than the cephalis, dilated around the wide open mouth, with a coronet of twenty-five to thirty slender basal feet, which are slightly curved and convergent, about as long as the thorax. Pores small, numerous and circular.

Dimensions.—Cephalis 0.05 long, 0.07 broad; thorax 0.06 long, 0.08 broad; horns 0.02 long, feet 0.06 long.

Cephalis nut-shaped, with deep sagittal and deep collar stricture, and with three stout divergent horns of nearly equal length. Thorax cylindrical, twice as long as the cephalis, and of the same breadth, with a coronet of twelve to sixteen broad, lamellar, rectangular, perpendicular feet around the mouth, about as long as the cephalis. Pores rather large, subregular, circular.

Genus 478. Desmospyris,^[96] Haeckel, 1881, Prodromus, p. 443.

Definition.—Phormospyrida with numerous basal feet (nine to twelve or more), without a coryphal horn.

The genus Desmospyris differs from the two preceding polypodal genera in the complete absence of horns on the coryphal face of the cephalis. It therefore corresponds to Gorgospyris among the Zygocyrtida, and arises when the numerous basal feet of the latter become connected by lattice-work.

Shell mammillate, with deep sagittal and slight collar constriction. Pores irregular, roundish. Cephalis nut-shaped, larger than the inversely conical thorax, and twice as broad as the constricted {1090}mouth. Coronet of the peristome with twelve to fifteen short conical convergent feet, shorter than half the thorax.

Shell smooth, with deep sagittal and collar strictures. Pores subregular, circular, double-contoured, very small and numerous. Cephalis nut-shaped, larger than the short truncate thorax. Coronet with eighteen to twenty-four slender, irregular, pointed, convergent feet, about twice as long as the thorax.

Petalospyris anthocyrtoides, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 533, 539, Taf. xxxii. fig. 19, a-c.

Shell tuberculate, with slight sagittal and sharp collar strictures. Pores subregular, circular. Cephalis nut-shaped, larger than the short truncate thorax. Coronet with fifteen to twenty short conical, parallel and vertical feet, about as long as the thorax.

Shell smooth, with slight sagittal and slight collar strictures. Pores subregular, circular, small and numerous. Cephalis campanulate, smaller than the ovate thorax. Coronet with fifteen to twenty irregular lamellar feet, which are longer than the thorax, pointed, nearly vertical and parallel.

Family LV. Androspyrida, n. fam. (Pl. 88-90).

Definition.—Spyroidea with galea and thorax; the shell composed of a bilocular cephalis and of two secondary joints, a galea arising from its upper face, and a thorax arising from its lower face.

The family Androspyrida differs from the three preceding families of Spyroidea in the three-jointed shell, in which the galea of the Tholospyrida and the thorax of the Phormospyrida are combined; it may therefore be derived from the latter by development of a galea, or from the former by formation of a thorax. The common ancestral group of these three families is probably the Zygospyrida. But it may be that a part of the Androspyrida has originated directly from the Stephoidea.

Two species only of this family were hitherto known, Amphispyris reticulata (figured, in 1872, by Ehrenberg, as Dictyospyris) and Sphærospyris sphæra (described, in 1882, by Bütschli, as Dictyospyris). Thirty new species were found in the collection of the Challenger, and are here disposed in seven genera. But perhaps these may represent three different families, which we here enumerate as subfamilies; the Lamprospyrida, Perispyrida, and Nephrospyrida.

The Lamprospyrida, the first subfamily, are tripodal Spyroidea with galea and thorax; they may therefore be regarded as a combination of Tholospyris and Acrospyris. In the simpler form, Androspyris (Pl. 83, fig. 8), the network of the shell is simple, and allows a very clear recognition of the internal structure. In the splendid Lamprospyris, derived from it (Pl. 89, figs. 13, 14) the delicate network is more or less spongy. The large apical horn is branched and fenestrated in the latter and simple in the former.

The Perispyrida, the second subfamily, possess no free apophyses, but a three-jointed shell with two distinct transverse strictures, an upper mitral and a lower collar stricture. The network of this shell is incomplete in Amphispyris (Pl. 88, figs. 2-7), being developed only in the frontal or lateral perimeter, thus making it probable that this subfamily may have arisen directly from the Tympanida (Toxarium, Pl. 88, fig. 1; Pl. 93, figs. 18-20). The network of Tricolospyris (Pl. 88, figs. 8-11) is complete, of another shape in the cephalis than in the galea and thorax; it is doubled or spongy in Perispyris (Pl. 88, figs. 12, 13).

The Nephrospyrida, the third subfamily, contains two very different genera only, each of which may represent a separate family. Sphærospyris (Pl. 83, fig. 4) possesses a spherical or subspherical lattice-shell, the central part of which includes a sagittal ring, connected with the inner face of the sphere by a number of paired apophyses, corresponding to those of Lithocircus; it may be easily confounded with some Sphæroidea (Carposphæra), but the enclosed ring leaves no doubt as to its true origin. Nephrospyris (Pl. 90) has a flat discoidal shell of considerable size, usually kidney-shaped or cordate, with a deep sagittal incision at the base, indicating the region where the pseudopodia are protruded from the porochora. The violin-shaped central capsule has two large lateral lobes on each side of the including sagittal ring, and the transverse nucleus is perpendicular to its sagittal plane (Pl. 90, figs. 7, 10). Sphærocircus as well as Nephrospyris have probably arisen independently from the Stephanida.

Synopsis of the Genera of Androspyrida.

Subfamily 1. Lamprospyrida, Haeckel.

Definition.—Androspyrida with three free basal feet (an odd posterior caudal foot and two paired anterior pectoral feet).

Genus 479. Androspyris,^[97] n. gen.

Definition.—Androspyrida with three free basal feet and a simple apical horn; lattice-work of the three-jointed shell simple, not spongy.

The genus Androspyris is probably the most original form of the Androspyrida, and represents, together with the following Lamprospyris, the subfamily of Lamprospyrida, which always possess three free basal feet, an odd posterior or caudal foot, and two paired anterior or pectoral feet. It may be derived either from Acrospyris by development of a cupola, or from Tholospyris by development of a thorax; the common ancestral form of these three typical genera is, no doubt, Tripospyris. Some species of Androspyris reach a considerable size and are distinguished by a peculiar external form resembling somewhat a human figure.

Shell thorny, with two deep transverse constrictions and irregular polygonal pores. Galea subspherical, with a strong pyramidal oblique horn, about two-thirds as large as the cephalis, which has the form of a human thorax, includes a strong ovate sagittal ring, and bears on each side a stronger lateral spine. Thorax short and broad, prolonged into three latticed divergent feet; the {1093}two lateral (pectoral) feet are like the legs of a human body, and are twice as long as the cephalis and as the tail-like caudal feet. (The whole shell exhibits a curious similarity to a human figure, more than in the following nearly allied species.)

Dimensions.—Length of the shell (including horn and feet) 0.4, breadth 0.1 to 0.15.

Shell rough, with two distinct transverse constrictions and irregular polygonal pores. Galea ovate, with a slender conical oblique horn, about as large as the cephalis, which exhibits a deep longitudinal furrow in the sagittal dorsal line. Thorax half as long, prolonged into three short latticed feet; the terminal spines of the two lateral feet are vertical and parallel, that of the caudal foot larger, directed obliquely backwards.

Dimensions.—Length of the shell (including horn and feet) 0.35, breadth 0.1 to 0.12.

Shell smooth, with two slight transverse constrictions. Galea conical, with a short conical horn, longer than the nut-shaped cephalis. Thorax with three nearly vertical and parallel feet of equal length. Pores in the galea and thorax very small and numerous, circular, in the cephalis much larger, irregular, roundish.

Dimensions.—Length of the shell (including horns and feet) 0.25, breadth 0.06 to 0.08.

Shell smooth, with two slight transverse constrictions and irregular, roundish pores. Galea hemispherical, with a short conical horn, about as large as the roundish cephalis and half as large as the ovate thorax. The three feet arise immediately beyond the collar stricture, are equal, divergent, curved, about as long as the cephalis, and are not terminal (as in the three preceding species), but lateral appendages of the thorax.

Genus 480. Lamprospyris,^[98] Haeckel, 1881, Prodromus, p. 447.

Definition.—Androspyrida with three free basal feet and a fenestrated apical horn; lattice-work of the three-jointed shell wholly or partly spongy.

The genus Lamprospyris differs from the preceding Androspyris, its ancestral form, mainly in the higher development of the lattice-work of the large shell. Whilst this in {1094}the latter genus is a simple lattice-plate, it here becomes more or less spongy, and sometimes forms a very dense and delicate wickerwork. The apical horn and the three basal feet are commonly also fenestrated. The two annular strictures, which separate the cephalis from the conical cupola and the inflated thorax, are commonly not so distinct as in the preceding genus. Some species belong to the largest Spyroidea and reach more than half a millimetre in length.

Shell nearly pear-shaped, with two distinct annular strictures, and uneven papillate surface. The total length is equal to twice the greatest breadth, and to seven times the length of the ring. Apical horn free, irregularly branched and fenestrated, as long as the included columella beyond it. The three diverging feet are strongly curved, S-shaped, and completely included by loose lattice-work. In the middle of their length they give off a simple strong lateral branch. The loose arachnoidal lattice-work is rather equally developed.

Dimensions.—Length of the entire shell (including the apophyses) 0.5, greatest breadth 0.25, ring 0.07 long.

Shell slender, pear-shaped, very similar to the preceding species, but differing in the following characters—the branched horn is much larger and twice as long as the columella; the two annular transverse strictures (separating the three joints) are deeper. The free internal branches of the three included feet are forked. Lattice-work looser than in the preceding species.

Shell ovate, spiny, with two slight annular transverse strictures; their length equal to one and a half times the breadth, and up to seven times the length of the ring. Apical horn quite included by the loose lattice-work of the large conical cupola, which is as long as the cephalis and thorax together. The three slender feet are also included in the lattice-work and only one-third as long as the shell, nearly vertical. Lattice-work much denser than in the two preceding species.

Shell ovato-conical, very similar to the preceding species, but smooth, not spiny. The apical horn and the three feet are much longer, not included in the network, but freely prominent, half {1095}as long as the shell and nearly vertical, parallel. The arachnoidal lattice-work is much denser in the middle third (cephalis) than in the upper third (cupola) of the lower third (thorax).

Dimensions.—Length of the shell (without appendages) 0.45, breadth 0.3, ring 0.08 long.

Shell slender, ovate, very similar to the preceding species; differing from it in the larger cupola, which is as long as the cephalis and thorax together. The three feet are much shorter and weaker, more divergent. This differs from all four preceding species in the possession of a large double apical horn; the two horns are strong, pyramidal, straight, strongly divergent, and as long as the cupola.

Dimensions.—Length of the shell (without the appendages) 0.3, breadth 0.2, ring 0.05 long.

Subfamily 2. Perispyrida, Haeckel, 1881, Prodromus, p. 443.

Definition.—Androspyrida without free basal feet, with three distinct joints separated by two parallel transverse strictures.

Genus 481. Amphispyris,^[99] Haeckel, 1881, Prodromus, p. 444.

Definition.—Androspyrida without free basal feet, with three distinct joints, separated by two transverse strictures; lattice-work of the shell only complete in the frontal ring, with large open holes on the ventral and dorsal face.

The genus Amphispyris and the two following genera arising from it, represent together the peculiar small subfamily of Perispyrida. This may have originated directly from Toxarium (family Tympanida, Pl. 88, fig. 1; Pl. 93, figs. 18-20), the large holes between its arches and rings becoming filled up by lattice-work; in Amphispyris this intercalated network remains incomplete on the ventral and dorsal faces, whilst in Tricolospyris it becomes complete, and in Perispyris spongy.

Subgenus 1. Amphispyrium, Haeckel.

Definition.—On each side of the ring-plane three pairs of large annular meshes; no middle zygomatic ring is developed between the two tympanic transverse rings (superior orbital and inferior maxillary ring).

Shell thorax-shaped, as long as broad, with a deep sternal incision and two slight transverse strictures. On each side of the ring-plane three pairs of large, irregular, annular holes of nearly equal size, the middle holes nearly half as broad as the shell. No zygomatic bars between the orbital and maxillary bars. Lateral lattice-girdle narrow, with few small roundish meshes.

Shell shaped like the "corpora quadrigemina cerebralia," with two deep crossed strictures, a coronal transverse stricture and a sagittal sternal stricture. On each side of the ring plane three pairs of large, irregular, annular, double holes, the middle holes larger than the upper and lower holes, and about one-fourth as long as the shell. No zygomatic bars between the orbital and maxillary bars. Lateral lattice-girdle broad, with numerous small meshes.

Dictyospyris reticulata, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 289, Taf. x. fig. 19.

Shell thorax-shaped, one and one-fifth times as long as broad, with a deep sternal incision and two distinct transverse strictures. On each side of the ring-plane three pairs of large annular holes of nearly equal size, about one-third as long as the shell. No zygomatic bars between the orbital and maxillary bars. Lateral girdle narrow, with few large polygonal meshes.

Subgenus 2. Amphispyridium, Haeckel.

Definition.—On each side of the ring-plane four pairs of larger annular meshes; a middle horizontal zygomatic ring is developed between the two tympanic transverse rings (superior orbital and inferior maxillary ring).

Shell thorax-shaped, one and one-fifth times as long as broad, with deep sternal incision and two distinct transverse (tympanic) strictures. On each side of the ring-plane four pairs of large irregular, annular holes; the fourth (inferior or buccal) pair is the longest. The middle of the sagittal ring {1097}is crossed by horizontal zygomatic bars (between the ascending orbital and the descending maxillary bars). Lateral lattice-girdle narrow, with few large meshes.

Shell compressed, nearly square, spiny, with slight sternal incision and two distinct transverse strictures. Similar to the preceding species; four pairs of irregular annular pores of nearly equal size. Zygomatic ring complete. Lateral lattice-girdle narrow, with few large meshes.

Shell compressed, nearly square, with slight sternal incision and two obliterated transverse strictures. Similar to the two preceding species; with four pairs of large annular pores, the two middle of which (the orbital and nasal holes) are much larger than the superior (frontal) and inferior (oral) holes. Zygomatic ring incomplete. Lateral lattice-girdle broad, with very numerous, small, irregular, polygonal pores.

Shell inflated, with deep sternal incision and two distinct transverse strictures. Similar to the preceding species, but with deeper constriction and looser lattice-work. Four pairs of large, irregular, annular pores, the central two of which are much larger. Zygomatic ring complete. Lateral girdle broad, with irregular pores of very different size.

Genus 482. Tricolospyris,^[100] Haeckel, 1881, Prodromus, p. 443.

Definition.—Androspyrida without free basal feet, with three distinct joints, separated by two transverse strictures; lattice-work of the shell complete, simple.

The genus Tricolospyris has arisen from the preceding Amphispyris, its ancestral form, by development of lattice-work which completely closes the large open holes remaining on the ventral and dorsal faces of the latter.

Shell smooth, one and a half times as long as broad, with two deep transverse strictures. Pores of the cephalis large, roundish, of nearly equal size. Cupola and thorax hemispherical, of about the same size and form, with numerous and small, double-contoured, roundish pores.

Shell spiny, twice as long as broad, with two deep transverse strictures. Pores of the cephalis large, roundish, polygonally framed, of very different size; two middle transverse rows of smaller pores enclosed between a superior and an inferior row of very large pores. Cupola and thorax hemispherical, about equal, with much smaller and very numerous roundish pores.

Shell rough, twice as long as broad, with two sharp strictures. Pores of the cephalis large, very irregular, partly lobated. Cupola hemispherical, smaller than the campanulate thorax, both with smaller irregular pores.

Shell spiny, slender, three times as long as broad, with two distinct strictures. Pores of the cephalis very large, irregular. Cupola hemispherical, only one-third as long as the slender inversely conical abdomen, both with irregular, much smaller pores.

Genus 483. Perispyris,^[101] Haeckel, 1881, Prodromus, p. 444.

Definition.—Androspyrida without free basal feet, with three distinct joints, separated by two transverse strictures; lattice-work of the shell double or spongy.

The genus Perispyris differs from the preceding Tricolospyris, its ancestral form, in the development of a secondary outer shell, which encloses the inner primary one either like an enveloping cortical shell or like a spongy veil. This is produced by the concrescence of meeting branches, which arise from spines of the inner shell.

Shell smooth, with two deep transverse annular strictures and a deep sagittal incision at the sternal base; one and a half times as long as broad. Cephalis nut-shaped, with large irregular roundish pores and very broad bars. Everywhere from its surface there arise numerous slender arborescent radial beams; by the anastomoses of their ramified branches there arise the flat cap-shaped cupola and the larger bilobed thorax; and also the external enveloping shell with loose delicate network.

Dimensions.—Inner shell 0.17 long, 0.1 broad; outer shell 0.23 long, 0.17 broad; ring 0.06 long.

Shell rough, with two distinct transverse strictures and a deep sternal incision, similar to the preceding; the radial beams arising from the inner shell, and forming by anastomosing branches the outer shell, are thinner and more numerous, and the framework of the latter on the surface is very dense and spongy, therefore the shell is dark and not transparent.

Dimensions.—Inner shell 0.18 long, 0.12 broad; outer shell 0.24 long, 0.18 broad; ring 0.08 long.

Shell smooth, lentelliptical, with three different isopolar axes, perpendicular one to another. Transverse and sagittal strictures are wanting; but the large enclosed ring and the two pairs of large adjacent annular meshes indicate clearly the position and size of the hidden cephalis. The two other joints (the cupola on the upper and the thorax on the lower pole of the cephalis) are nearly equal, cap-shaped or hemispherical. The outer lentelliptical shell is little larger than the inner, connected with it by numerous thin bristle-shaped radial beams, and exhibits a delicate arachnoidal lattice-work.

Dimensions.—Inner shell 0.15 long, 0.1 broad; outer shell 0.18 long, 0.13 broad; ring 0.08 long.

Subfamily 3. Nephrospyrida (vel Paradictyida, Haeckel, 1881).

Definition.—Androspyrida without free basal feet and external constrictions. Shell either spherical or discoidal.

Genus 484. Sphærospyris,^[102] n. gen.

Definition.—Androspyrida with a spherical or subspherical shell, without basal incision and transverse constriction; without free basal feet.

The genus Sphærospyris differs from all other Spyroidea in the regular spherical or spheroidal form of the lattice-shell. It may therefore be easily confounded with some species of the Sphæroidea; but the internal sagittal ring, placed in the median plane of the fenestrated sphere and connected with it by radial beams, leaves no doubt that it is derived from a true Spyroid, either Dictyospyris or Amphispyris, or another genus. Sometimes also four larger collar pores are visible.

Dictyospyris sphæra, Bütschli, 1882, Zeitschr. f. wiss. Zool. vol. xxxvi. pp. 511, 539, Taf. xxxii. fig. 15, a, b.

Shell smooth, nearly spherical, slightly flattened at the base, with small regular circular pores. In the centre of the basal plate a regular rectangular cross with four equal collar pores.

Shell rough, nearly spherical, slightly flattened at the base, with small regular circular pores. In the centre of the basal plate a bilateral symmetrical cross with four ovate collar pores; two cardinal pores twice as large as the two jugular pores and six to eight times as broad as the other shell-pores.

Shell smooth, perfectly spherical, with small subregular circular pores. In the centre of the basal plate no larger collar pores. (The original collar pores are here of the same size as the other pores, and cannot therefore be distinguished.)

Genus 485. Nephrospyris,^[103] Haeckel, 1881, Prodromus, p. 444.

Definition.—Androspyrida with a discoidal, kidney-shaped, or subcircular shell, with a basal incision; without transverse constriction and free basal feet.

The genus Nephrospyris is one of the most peculiar and most modified of the Spyroidea, of extraordinary size, in this respect surpassing all other genera of this {1101}suborder, and differing from them in its flat discoidal form. The diameter of the compressed shell often reaches one half millimetre or more; its perimeter is elliptical or nearly circular, smooth, constantly with a characteristic deep sternal incision or a basal sinus on the basal pole of the main axis. The central sagittal ring is comparatively small. The margin is often inflated like a delicate reticular girdle, and contains a large number of peculiar spherical or roundish nucleated cells (Pl. 90, figs. 6-10). According to the observations of Dr. John Murray, made on living Nephrospyris, they are Vorticellina, perhaps constant Symbiontes.

Subgenus 1. Nephrodictyum, Haeckel, 1881, Prodromus, p. 444.

Shell kidney-shaped, one and a half times as broad as long, and three times as long as the deep kidney-shaped sternal incision. Ring with six pairs of branched apophyses, the bars of the apical pair vertical, of the basal pair divergent. The corresponding bars of the two middle pairs (on the frontal and the occipital face) form together on each side a large pentagonal or hexagonal naso-orbital area, which is surrounded by four or five large polygonal meshes; the other meshes become smaller towards the inflated margin. All meshes simple, without arachnoidal framework.

Shell kidney-shaped, one and two-third times as broad as long, very similar to the preceding species (or only a variety of it?). Ring with seven pairs of branched apophyses. The large naso-orbital area is on the dorsal or occipital side simple, on the ventral or facial side divided by an equatorial pair of transverse horizontal branches into two superior orbital, and two inferior nasal holes. Sternal incision ovate. All meshes simple.

Dimensions.—Shell 0.25 to 0.35 long, 0.4 to 0.5 broad; ring .007 to 0.08 long.

Shell kidney-shaped, twice as broad as long, very similar to the two preceding species (or only a variety of them?). Ring with eight pairs of branched apophyses. The large naso-orbital area (between the mitral and collar ring) is on the dorsal and on the ventral side divided by two equatorial pairs of horizontal branches into two superior (orbital and occipital), and two inferior (nasal and suboccipital) holes. Sternal incision cordate. All meshes simple.

Shell heart-shaped, about as long as broad. Ring with six pairs of branched apophyses (as in Nephrospyris renilla, Pl. 90, fig. 9). No equatorial transverse branches. Sternal incision cordate, deeper than in all other species of the genus, nearly half as long as the shell. All meshes of the network simple.

Subgenus 2. Paradictyum, Haeckel, 1881, Prodromus, p. 444.

Definition.—Network of the shell double; the larger meshes separated by strong bars, and filled up by a very delicate secondary arachnoidal network.

Paradictyum paradoxum, Haeckel, 1881, Prodromus et Atlas, loc. cit.

Shell nearly circular, ten times as broad as the inflated marginal girdle, and three times as long as the sternal incision. Ring with six pairs of branched apophyses; the bars of the apical pair nearly vertical, of the basal pair divergent; the corresponding and opposite bars of the two middle pairs (on the occipital and on the frontal face) form together a large middle naso-orbital area; above and below this lie six pairs of larger meshes. All larger meshes of the network are filled up by very delicate arachnoidal framework. The inflated and delicately reticulated marginal girdle of this and of the following closely allied species is usually filled up by nucleated roundish cells (fig. 7), which are Vorticellinæ, according to the observations of Dr. John Murray on living specimens.

Dimensions.—Diameter of the shell 0.5 to 0.6, of the marginal girdle 0.05 to 0.07; ring 0.07 to 0.09 long.

Shell kidney-shaped, one and one-third times as broad as long, six times as broad as the inflated marginal girdle, and half as long as the sternal incision. Ring with six pairs of apophyses. Above and below the large naso-orbital holes lie ten pairs of larger meshes. All the meshes are filled up by very delicate arachnoidal network.

Dimensions.—Length of the shell 0.4 to 0.5, breadth 0.5 to 0.7; ring 0.06 to 0.08 long.

Suborder II. Botryodea, Haeckel, 1881 (Pl. 96).

Polycyrtida, Haeckel, 1862, Monogr. d. Radiol., p. 341.

Polycyrtida, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 519.

Botryodea (= Botrida vel Botryida), Haeckel, 1881, Prodromus, p. 439.

Definition.—Nassellaria with a complete lattice-shell, exhibiting constantly a lobate and multilocular cephalis, with three to five or more separated lobes, and two to three or more constrictions.

The suborder Botryodea differs from the other Cyrtellaria in the multilocular and lobate shape of the cephalis, which is composed of at least three or four, often five or six, and sometimes even a greater number of lobes, which are separated by constrictions and partly also by internal septa. This characteristic shape is found neither in the Spyroidea (with bilocular cephalis) nor in the Cyrtoidea (with simple cephalis). The affinities of the former group to the two latter form a very complicated problem, which is not yet solved; the morphology of the Botryodea is the most difficult part in the system of Nassellaria, and what we can here give, are incomplete and unsatisfactory beginnings only.

Up to the year 1860 only a single genus of the Botryodea was known, Lithobotrys, one of the oldest genera of "Polycystina," and described by Ehrenberg in 1844 (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 74). He gave the following definition:—"Loricæ siliceæ articuli in adulto non in seriem, sed in uvæ brevis formam, id est in loculos plus minus discretos nonnullos contiguos dispositi. Proxime ad Lithocampem accedit." In his first System (1847) Lithobotrys is placed with Lithocampe among his family Lithochytrina. Afterwards (1860) Ehrenberg added two new genera, under the names Botryocampe and Botryocyrtis and figured some species of these incompletely in his last works (1872, 1875).

In my Monograph I founded for these three genera the separate subfamily of Polycyrtida, added as a fourth genus Spyridobotrys, and gave to the group the following definition (1862, loc. cit., p. 341):—"Lattice-shell divided by two or more annular strictures, partly longitudinally, partly transversely, into three or more unequal chambers, which are placed in different planes and have a different relation to the poles of the shell-axis."

The new and remarkable forms of Botryodea, which I subsequently found in the Challenger collection, demonstrated that the Botryodea differ from the other Cyrtellaria (the Cyrtoidea as well as the Spyroidea) in a far higher degree than I formerly had supposed. A synopsis of the figures in Pl. 96 will give sufficient evidence of this view. Therefore in my Prodromus (1881, p. 439) {1104}I completely separated the Botryodea (or Botrida) from the other suborders of Cyrtellaria (Spyrida and Cyrtida).

Bütschli gave, in 1882, in his paper on the Cyrtida (loc. cit.) a very accurate description of Lithobotrys geminata, and pointed out its close affinity to Lithocorythium and Lithomelissa, and the importance of an oblique septum separating the cephalis into a smaller anterior and a larger posterior lobe. His views on the Botryodea (as a subordinate group of the Cyrtoidea) are however incomplete, since the peculiar forms, described in the following pages, were unknown to him.

According to the wide morphological divergence of the different Botryodea, and the numerous peculiar forms developed from it, we here divide the whole group into three families and ten genera, with fifty-five species. These form, however, only a small part of the large and varied mass of closely related forms which are found in the rich collections of the Challenger. The great difficulty of researches on their intimate structure, and the great amount of time required for it, prevented me from giving a more complete and exact description than the one here given. The observation of the small shells from all the different sides is a difficult task, requiring years of work, and its satisfactory explanation would be possible only by means of numerous figures.

The three families of Botryodea, here described, correspond to the three first groups of Cyrtoidea. The first family, Cannobotryida, corresponds to the Monocyrtida clausa and to the Zygospyrida; their shell consists of a cephalis only, without subsequent joints. The second family, Lithobotryida, corresponds to the Dicyrtida and Phormospyrida; their shell is composed of a cephalis and a thorax, both joints being separated by a transverse cortinar septum and a collar stricture. The third family, Pylobotryida, has a three-jointed shell, like the Tricyrtida, with cephalis, thorax and abdomen.

The cephalis is the most characteristic part of the shell of the Botryodea and its lobulate and multilocular shape separates them from the Spyroidea and Cyrtoidea. It represents the whole shell in the Cannobotryida, and in the young state of the two other families, which afterwards develop a thorax (Lithobotryida) and an abdomen (Pylobotryida). The typical lobulation of the cephalis is probably originally caused by internal septa; and these may be originated by branches of the internal columella, which corresponds either to the central ascending columella of the Plectoidea or to the excentric ascending dorsal rod of the sagittal ring of the Stephoidea. But afterwards, when the original septa disappear and are lost by reduction, only the external constrictions remain to indicate the limits of the single lobes.

Among the internal septa and the corresponding external constrictions which effect the lobulation of the cephalis, may be distinguished primary or constant septa and secondary or inconstant septa. As primary septa we regard firstly an oblique frontal {1105}septum and secondly a vertical sagittal septum. The frontal septum (described accurately by Bütschli) has usually two or three pairs of pores and ascends obliquely from the base to the anterior face of the cephalis, where it is inserted in the orbital region; it divides the cephalis into a smaller anterior or facial lobe and a larger posterior or occipital lobe. The latter is commonly higher and more developed than the former and partly covers its upper face, like the crest of a helmet. The facial lobe is again bisected by an incomplete sagittal septum and a corresponding partial constriction on the anterior face. We find, therefore, in this original cephalis of the Botryodea, three primary lobes, an odd larger occipital lobe and two paired smaller facial lobes. The typical trilobed cephalis may be regarded perhaps as the common original form of the Botryodea.

The secondary and inconstant constrictions which we find in many Botryodea, and which produce a greater number of lobes in the cephalis, require further accurate observation. The following cases of lobation may be considered as the most important:—(1) Cephalis with four lobes, opposite in two pairs (two larger occipital and two smaller facial lobes, separated by a complete sagittal and an oblique frontal constriction); (2) cephalis with four unequal lobes, two of which are odd and sagittal, two paired and lateral (the odd occipital lobe usually larger and the odd mandibular lobe smaller than the two paired lateral or buccal lobes); (3) cephalis with five lobes (a large odd occipital lobe and two pairs of smaller lobes, anterior nasal, and lateral buccal lobes); (4) cephalis with five lobes, three of which are odd (a posterior occipital, middle frontal, and anterior facial lobe), and one pair of lateral lobes; (5) cephalis with six lobes, opposite in pairs (two larger occipital, two smaller nasal and two intermediate lateral or buccal lobes); (6) cephalis with six lobes, two of which are odd and sagittal (a large occipital and a smaller nasal lobe), four opposite in pairs (two anterior and two posterior buccal lobes); (7) cephalis with seven lobes, three of which are odd (a large posterior occipital, a middle frontal, and an anterior small nasal lobe), four opposite in two pairs (an anterior buccal and a posterior temporal pair); (8) cephalis with eight lobes, two of which are odd (a large posterior occipital and a small anterior frontal lobe) and six opposite in three lateral pairs; (9) cephalis with nine lobes, three of which are odd (an occipital, a frontal and a nasal lobe) and six opposite in three lateral pairs; (10) cephalis with ten lobes, two of which are odd (a large occipital and a smaller frontal lobe) and the other eight opposite in pairs; (11) cephalis with numerous lobes (twelve to fifteen or more) which are symmetrically disposed on each side of the median plane; (12) cephalis with numerous lobes (twelve to fifteen or more) which are irregularly and sometimes spirally conglomerated.

All these different forms of lobation require a far more thorough examination than I can devote to them, and may furnish examples of regular laws of development. The irregular forms are rather common, and I have found some very irregular Botryodea {1106}(not here described) in which I could not determine the topographical regions of the cephalis. The difficulty in the examination of these complicated forms is increased by their very small size, which does not reach the usual dimensions of the other Cyrtellaria. In some cases I was able to observe on the base of the cephalis the same typical cortinar pores (in two or three pairs), which we also find in the same part of the cephalis in the Spyroidea and Cyrtoidea, and which are inherited from the Semantida.

The thorax of the Botryodea, or the second shell-joint, absent in the Cannobotryida, is usually of very simple form, ovate, truncate, conical or cylindrical, and consists of a secondary joint, developed from the base of the cephalis. The thorax is usually small, about the same size as the cephalis or a little larger, whilst in the Cyrtoidea it is commonly much larger than the latter. Its terminal mouth is closed by a lattice-plate in the Botryocellida, while it remains open in the Botryopylida and Pylobotryida.

The abdomen, or the third shell-joint, developed in the Pylobotryida only, generally also exhibits a very simple shape, like the thorax, and it is a tertiary joint developed from the base of the thorax. It exhibits to the latter the same relation as in the Tricyrtida. The terminal mouth of the abdomen remains open in the Botryocyrtida; it becomes closed by a lattice-plate in the Botryocampida.

The lattice-plate forming the shell of the Botryodea is usually very thin and fragile, with very small circular pores. These are often very numerous, at other times scarce, and sometimes nearly wanting, so that the shell appears hyaline. In this group there never occurs that great variety in form and size of the pores, which numerous Cyrtoidea and Spyroidea exhibit.

The radial apophyses which are found in the majority of Botryodea seem to correspond in position and relation to the typical radial beams of the other Nassellaria, viz., three descending basal feet arising from the base of the cephalis, and an ascending vertical apical horn arising from the top of the cephalis. Here also they seem to be inherited from the Plectoidea or Stephoidea (Cortina, Cortiniscus). But whilst these four typical radial beams in the other Nassellaria are usually simple spines or solid rods, here they usually appear as hollow cylindrical tubes, the thin wall of which is pierced by the same small pores as the shell. These porous tubes are either straight or slightly curved, often inflated and ovate at the base. We find in their number and disposition the same variety as in the simple radial spines of the other Nassellaria. The original number may here also be seen in the development of four typical beams, an ascending apical tube on the top of the cephalis, and three descending basal tubes on its base; the odd posterior tube of the latter corresponds to the caudal foot, the two paired anterior to the pectoral feet. There is often also a fourth foot developed opposite to the caudal, and representing a sternal tube. Sometimes also two superior tubes are developed, a posterior occipital and an anterior frontal. The different {1107}apophyses may be lost by reduction. I have never observed Botryodea with more than five apophyses.

The Central Capsule of the Botryodea is not yet sufficiently known, no living species having been observed. In some preparations from specimens in the Challenger collections, stained by Dr. John Murray with carmine immediately after the dredging operation, single Botryodea are to be found in which the central capsule is deeply coloured. In Botryopera quinqueloba (Pl. 96, fig. 2) it filled up the greater part of the cephalis and seemed to be divided into some small lobes. In Lithobotrys sphærothorax (Pl. 96, fig. 15) it was divided into four lobes, three of which filled the trilobed cephalis, the fourth large lobe occupying a great part of the spherical thorax. Details of their structure, unfortunately, were not recognisable. There can, however, be no doubt that they are the same as in all other Nassellaria.

Synopsis of the Families of Botryodea.

Family LVI. Cannobotryida, Haeckel (sensu emendato).

Cannobotryida, Haeckel, 1881, Prodromus, p. 440.

Definition.—Botryodea monothalamia, the shell of which represents a lobate cephalis, without thorax and abdomen.

The family Cannobotryida (retained here with a stricter definition than originally was given in my Prodromus) comprises those Botryodea, in which the whole shell is represented by the cephalis alone, without thorax and abdomen. Since the two latter joints, found in the two following families, are secondary productions, the Cannobotryida must be regarded as the ancestral forms of all Botryodea, in an ontogenetic as well as in a phylogenetic sense.

Two species only of this family have been hitherto known, incompletely described by Ehrenberg as Lithobotrys triloba and Lithobotrys quadriloba. A great number of similar forms are to be found in the Radiolarian ooze of the Central Pacific, but they are very minute, and difficult to examine. We can describe here only twelve species of these, which we arrange in two genera; Botryopera without porous tubes, and Cannobotrys bearing a variable number of porous cylindrical tubes (one to five). The number of lobes of the cephalis is also variable in each genus (one to five or more). If in the future these minute and interesting shells should be better examined, it would {1108}be advisable to distinguish a number of genera according to the different number of the porous tubes and of the lobes of the cephalis. The base of the latter is constantly closed by a basal lattice-plate, and usually exhibits two or three pairs of cortinar pores, identical with those of the Semantida.

The phylogenetic origin of the Cannobotryida may be found either in the Zygospyrida or in the Monocyrtida; they differ from these two similar groups in the lobation of the cephalis, which is effected by the development of internal septa and external constrictions.

Synopsis of the Genera of Cannobotryida.

Genus 486. Botryopera,^[104] n. gen.

The genus Botryopera is the simplest form among the Botryodea, the shell consisting of a lobate cephalis only, without tubes or radial appendages. It may be derived either from Dictyospyris or from Archicapsa by development of the horizontal fold in the frontal face of the shell, and the corresponding internal frontal septum, which separates the larger occipital lobe from the smaller facial half; the latter may be divided again into paired frontal lobes, lateral buccal lobes, &c. Botryopera may be the common ancestral form of many Botryodea.

Cephalis trilobate; the posterior odd occipital lobe helmet-shaped, about twice as large as the two paired anterior frontal lobes, which are subovate and covered by the upper half of the former. Pores small and numerous, subregular, circular; some larger pores at the base.

Lithobotrys triloba, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 30.

Cephalis trilobate; the occipital lobe subcylindrical, one and a half times as long as the two frontal lobes, which are slender, ovate and not covered by the former. Pores small and numerous.

Habitat.—Fossil in Tertiary rocks of the Mediterranean (Sicily, Greece, &c.)

Lithobotrys quadriloba, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 84.

Cephalis quadrilobate; the occipital lobe helmet-shaped, one and a half times as long as the two paired hemispherical buccal lobes, and twice as large as the anterior frontal lobe. Pores not numerous, rather large, circular.

Cephalis quinquelobate; the occipital lobe helmet-shaped, and twice as long as the two hemispherical frontal lobes, three times as long as the subspherical lateral buccal lobes. Pores scarce, small, circular.

Cephalis multilobate; the posterior odd occipital lobe ovate, and of about the same size as the anterior frontal half of the shell, which is clustered and divided into five to seven smaller lobes, an odd subspherical sternal lobe, and on each side of it two or three pairs of smaller subspherical lobes.

Genus 487. Cannobotrys,^[105] Haeckel, 1881, Prodromus p. 440.

The genus Cannobotrys differs from the preceding Botryopera in the development of hollow radial tubes, arising from the lobate cephalis in various numbers. According to their number the genus may be divided into various subgenera: (1) Cannobotrantha (monocanna) with a single apical tube; (2) Cannobotrella (dicanna) with two divergent tubes, an ascending apical and a descending sternal one; (3) Cannobotrissa (tricanna) with three tubes in the sagittal plane (an upper apical, a posterior caudal, and an anterior sternal); (4) Cannobotromma (tetracanna) with four radial tubes disposed like the four typical spines of Cortina (compare p. 950), and Cannobotrusa (pentacanna) with five radial tubes disposed like the five typical spines of Stephanium (p. 952). {1110}Perhaps these five groups may be separated as five genera, possessing near relations to five very different genera of Nassellaria (Circospyris, Halicapsa, Archibursa, Cortina, Stephanium, &c.)

Cephalis trilobate, with a single cylindrical straight apical tube on the apex of the occipital lobe, which is helmet-shaped, and about one and a half times as long as the two subspherical frontal lobes. Pores small and numerous, subregular, circular.

Cephalis quadrilobate, with two divergent tubes, an odd apical tube on the apex of the posterior occipital lobe, and an odd sternal tube on the anterior frontal lobe. Between these two odd lobes lie two paired lateral or buccal lobes, of about the same size. Shell nearly hyaline, with very few minute pores.

Cephalis quinquelobate, with three curved cylindrical tubes in the sagittal plane; an ascending apical tube on the apex of the helmet-shaped occipital lobe, and two horizontal tubes on the base of the shell (a posterior caudal, c, and an anterior sternal, z). The two frontal lobes are hemispherical, and twice as large as the two lateral buccal lobes. Pores very small and numerous.

Cephalis multilobate, with three straight divergent cylindrical tubes in the sagittal plane; a vertical apical tube on the apex of the ovate occipital lobe, and two horizontal tubes on the base, as in the preceding similar species; it differs from the latter in the greater number of lobes (seven or nine), the two frontal lobes being divided into two or four secondary lobules.

Cephalis quinquelobate, with four cylindrical nearly straight tubes of equal size; an ascending, nearly vertical, apical tube on the apex of the occipital lobe, and three divergent descending tubes {1111}on the base of the shell (an odd posterior caudal tube and two paired anterior pectoral tubes). The two lateral buccal lobes are twice as large as the two anterior frontal lobes, and half as large as the posterior odd occipital lobe. The four tubes in this and the following species correspond probably to the four spines of Cortina (p. 950).

Cephalis multilobate, with four cylindrical curved tubes conical at their wider base, corresponding to those of the preceding species and to the four spines of Cortina. The odd occipital lobe is of about the same size as the anterior part of the shell, which is cleft into three pairs of roundish lobes, one pair of anterior larger frontal lobes, and two pairs of smaller lateral buccal lobes. Pores very few and minute.

Cephalis quinquelobate, with five cylindrical slender curved tubes, three of which are placed in the sagittal plane (a superior apical, a posterior caudal, and an anterior sternal), whilst the other two are paired and diverge laterally (two pectoral tubes). The five tubes correspond exactly to the five typical spines of Stephanium (p. 952). The helmet-shaped occipital lobe of the shell is twice as large as each of the two anterior frontal lobes, and three times as large as each of the two lateral buccal lobes. Pores numerous.

Family LVII. Lithobotryida, n. fam.

Definition.—Botryodea dithalamia, the shell of which is composed of a lobate cephalis and a simple thorax, without abdomen.

The family Lithobotryida comprises those Botryodea in which the shell is divided by a transverse annular constriction into a lobate cephalis and a simple thorax. They correspond therefore to the Dicyrtida among the Cyrtoidea, and to the Phormospyrida among the Spyroidea. The thorax, or the second shell-joint, is in all these three families a secondary production, arising from the base of the cephalis; therefore the Lithobotryida must be phylogenetically derived from the Cannobotryida.

Several species of Lithobotrys were first described by Ehrenberg as Lithobotrys and Lithocorythium. These two genera are, however, identical, as has been {1112}demonstrated by Bütschli (1882, loc. cit., p. 519). Some other species united by Ehrenberg with Lithobotrys belong to other genera. The number of Lithobotryida found in the "Radiolarian ooze" of the Challenger collection, is far greater than that of the Cannobotryida and Pylobotryida. But only a small part of them could be thoroughly examined and described here, so that their number may be greatly augmented by further accurate researches. We here arrange those forms in four genera, representing two different subfamilies. The terminal mouth of the thorax remains open in the Botryopylida, whilst it becomes closed by a lattice-plate in the Botryocellida. In each group there are shells with and without porous tubes. The number of these tubes, and also the number of lobes of the cephalis, is very variable, and may in future serve for the distinction of more genera.

Synopsis of the Genera of Lithobotryida.

Genus 488. Botryopyle, Haeckel, 1881, Prodromus, p. 440.

Definition.—Lithobotryida without tubes on the cephalis, and with the mouth of the thorax open.

The genus Botryopyle comprises the simplest forms of Lithobotryida, the lobate cephalis bearing no tubes and the basal mouth of the thorax remaining open. It may be derived either from Dictyocephalus or from Desmospyris, by development of lobes on the cephalis and of an internal frontal septum, separating the larger occipital lobe from the smaller frontal half of the shell. The latter may be divided again into anterior frontal lobes, lateral buccal lobes, &c.

Cephalis trilobate, separated by a deep collar constriction from the hemispherical thorax, which is twice as broad. Occipital lobe helmet-shaped, little longer than the two hemispherical frontal lobes. Surface spiny. Pores irregular, roundish, of very different size.

Lithobotrys cribrosa, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. iii. fig. 20.

? Lithobotrys biceps, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 295, Taf. ix. fig. 23.

Cephalis trilobate, separated by a slight collar constriction from the ovate thorax, which is somewhat smaller. Occipital lobe very large, helmet-shaped, longer than the thorax and twice as long as the two subspherical frontal lobes. Pores regular, circular, scarce.

Lithocorythium cephalodes, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iv. fig. 6.

Cephalis quinquelobate, separated by a slight collar constriction from the larger conical thorax, which is gradually dilated towards the wide mouth. Occipital lobe helmet-shaped, little longer than the frontal half of the cephalis, which is divided into two pairs of lateral chambers, corresponding to the four crossed pores of the sagittal septum, figured by Ehrenberg. The figure of the latter is inverse, seen from the frontal face, a part of the frontal wall having been broken off.

Cephalis multilobate, separated by an oblique constriction from the subcylindrical thorax, which is somewhat larger and slightly curved. Occipital lobe conical, of the same length as the posterior part of the triangular frontal half of the shell, which is divided into five to seven lobes, two or three odd lobes in the median part, and one or two pairs of lateral lobes; very variable in size and form of the lobes. Mouth of the thorax wide, truncate.

Cephalis multilobate, campanulate, separated by a sharp constriction from the inflated thorax, which is nearly twice as long and broad. Both joints of the shell are irregularly lobate, with numerous vaulted lobes of different sizes, and partly internal septa. Pores small and numerous.

Genus 489. Acrobotrys, Haeckel,^[106] 1881, Prodromus, p. 440.

Definition.—Lithobotryida with tubes on the cephalis, and with the mouth of the thorax open.

The genus Acrobotrys differs from the preceding Botryopyle in the development of radial tubes, and from its probable ancestral form, Cannobotrys, in the development of a thorax, the basal mouth of which remains open. According to the varying number of the tubes we may distinguish the following five subgenera (corresponding to those of Cannobotrys), viz., (1) Acrobotrantha (monosolenia) with a single (apical) tube; (2) Acrobotrella (disolenia) with two divergent tubes (an apical and a sternal); (3) Acrobotrissa (trisolenia) with three sagittal tubes (an apical, a caudal, and a sternal); (4) Acrobotromma (tetrasolenia) with four tubes, like the four typical spines of Cortina; and (5) Acrobotrusa (pentasolenia) with five feet, corresponding to the five typical spines of Stephanium.

Cephalis trilobate, with a single straight apical tube, which ascends vertically from the apex of the occipital lobe, and is pointed at the distal end, with an anterior oblique aperture. Two frontal lobes paired, ovate, half as long as the helmet-shaped occipital lobe. Thorax ovate, twice as long as the cephalis. Pores very scarce.

Cephalis trilobate, with three odd ovate lobes of nearly equal size in the sagittal plane and two divergent straight slender cylindrical tubes, a vertical apical tube on the occipital lobe, and a horizontal nasal tube on the frontal lobe; the middle lobe between them is somewhat smaller. Thorax ovate, about twice as large as the cephalis, with constricted mouth. Pores small and numerous.

Cephalis quinquelobate, with two divergent long cylindrical curved tubes. Occipital lobe helmet-shaped, with an ascending apical tube; nasal lobe conical, with a descending sternal tube; {1115}between them a smaller odd middle lobe, and on each side of the latter an ovate frontal lobe. Thorax inflate, twice as long and broad as the cephalis. Pores small, scarce.

Cephalis sexlobate, with two divergent tubes. Occipital and frontal lobes ovate, odd; between them a cupola-shaped apical lobe, bearing an ascending pointed apical tube. On each side at the base a small buccal lobe, and between the paired buccal lobes an anterior nasal lobe with a descending curved sternal tube. Thorax smaller than the cephalis. Pores numerous and small.

Cephalis quadrilobate, with three pointed and auriculate tubes, two ascending apical (an anterior and a posterior) in the helmet-shaped occipital lobe, and a descending sternal tube on the base of the frontal lobe; between the lobes two lateral paired buccal lobes. Thorax campanulate, twice as broad as the cephalis. Pores rather large and numerous.

Cephalis quadrilobate, with four odd lobes and three divergent curved tubes, an ascending apical tube in the conical occipital lobe, and two descending tubes on the anterior and posterior basal lobes; between these three lobes a small central lobe. Thorax ovate, about as large as the cephalis. Pores small and numerous.

Cephalis trilobate, with four slender cylindrical tubes. Occipital lobe helmet-shaped, with an apical tube on the apex and a caudal tube on the base. Two frontal lobes ovate, prolonged into two paired pectoral tubes. The four tubes correspond in position to the four spines of Cortina. Thorax inflate, ovate, larger than the cephalis. Pores very scarce, rather large, irregular.

Cephalis quinquelobate, with five short conical tubes; three divergent odd tubes arise from three odd lobes; an apical from the occipital lobe, a posterior caudal from the suboccipital lobe, and an {1116}anterior sternal from the nasal lobe. Two paired lateral tubes arise from the base of two ovate frontal lobes. The five tubes correspond in disposition to the five spines of Stephanium. Thorax truncate. Pores small.

Genus 490. Botryocella,^[107] Haeckel, 1881, Prodromus, p. 440.

Definition.—Lithobotryida without tubes on the cephalis, and with the mouth of the thorax closed.

The genus Botryocella differs from the closely allied Botryopyle in having the mouth of the thorax closed, and may be derived from it by development of a lattice-plate, effecting this closure. It bears therefore the same relation to the latter that Dicolocapsa has to Dictyocephalus.

Lithobotrys nucula, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. iii. fig. 16.

Lithobotrys adspersa, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. iii. fig. 15.

Cephalis trilobate; occipital lobe helmet-shaped, nearly twice as long as the two ovate frontal lobes. Thorax about as long as the cephalis. Pores very small and scarce.

Lithobotrys borealis, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 294, Taf. ii. fig. 3.

Cephalis trilobate; occipital lobe ovate, little longer than the two ovate frontal lobes. Thorax about twice as long as the cephalis. Pores very numerous and small.

Cephalis trilobate, with three odd sagittal lobes; the middle or central lobe larger than the anterior frontal and smaller than the posterior occipital lobe. Thorax nearly spherical, about as long as the cephalis. Pores small and scarce.

Cephalis quadrilobate; the helmet-shaped occipital lobe twice as long as the two paired subspherical buccal lobes, and three times as long as the odd spherical frontal lobe. Thorax nearly spherical, about as long as the cephalis.

Cephalis quadrilobate, with two pairs of lateral ovate lobes and complete sagittal constriction; the two occipital lobes nearly twice as large as the two frontal lobes. Thorax ovate, separated from the cephalis by a collar septum with four cortinar pores (fig. 14).

Cephalis multilobate; occipital lobe helmet-shaped, very large, about twice as long and broad as the frontal half of the shell, which is divided into six to eight small roundish clustered lobes. Thorax subspherical, of about the same size as the cephalis.

Genus 491. Lithobotrys,^[108] Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 74.

Definition.—Lithobotryida with tubes on the cephalis, and with the mouth of the thorax closed.

The genus Lithobotrys, the oldest and first known of the Botryodea, was founded by Ehrenberg in 1844, and was one of his five oldest genera of Polycystina. It represented by itself the suborder Botryodea until the year 1860. The numerous species described by Ehrenberg belong to very different genera of Botryodea, and partly also of Spyroidea. Following Bütschli (1882) we retain here the name Lithobotrys for those species, the type of which is Lithobotrys geminata. The genus Lithocorythium of Ehrenberg is for the greater part identical with it. When in the preceding genus Acrobotrys the mouth of the thorax becomes closed by lattice work, Lithobotrys arises. In the latter as well as in the former the number of tubes on the cephalis is different, and may characterise different subgenera.

Lithobotrys geminata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. iii. fig. 19.

Lithobotrys geminata, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi, p. 519, Taf. xxxiii. fig. 27, a to c.

? Lithocorythium platylophus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iv. fig. 5.

Cephalis trilobate, with a single apical tube in the apex of the helmet-shaped occipital lobe, which is one and a half times as long as the two subspherical frontal lobes. Thorax ovate, one and a half times as long as the cephalis, with few small pores in six to eight transverse rows.

Lithocorythium oxylophus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iv. figs. 3, 4.

? Lithopera oxystauros, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iii. fig. 6.

Cephalis trilobate, with a single apical horn or a pointed tube in the apex of the helmet-shaped occipital lobe, which is a little longer than the two ovate frontal lobes. Thorax ovate, about as long as the cephalis, with very numerous and small pores.

Lithobotrys nasuta, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. iii. fig. 21.

Cephalis quadrilobate, with a single descending sternal or nasal tube on the base of the anterior or frontal lobe, which is half as long as the helmet-shaped occipital lobe and twice as large as the two lateral buccal lobes. Thorax ovate, twice as long as the cephalis. Pores rather large, circular.

Lithobotrys ornata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. iii. fig. 18.

Cephalis quinquelobate, with two divergent ascending tubes, a posterior occipital and an anterior sternal or nasal tube. Occipital lobe campanulate, twice as large as the two frontal, and four times as large as the two buccal lobes. Thorax ovate, twice as long as the cephalis. Pores scarce and small. The specimen figured by Ehrenberg is very incomplete.

Cephalis trilobate, with two divergent cylindrical tubes, an ascending apical tube in the apex of the ovate occipital lobe, and a descending sternal or nasal tube in the campanulate frontal lobe; between the two lobes a smaller central lobe. Thorax spherical, twice as long as the latter. Pores very small, numerous.

Cephalis sexlobate, with two divergent cylindrical tubes, an ascending apical tube in the apex of the helmet-shaped occipital lobe and a descending sternal tube on the base, between the two kidney-shaped frontal lobes. The latter are half as large as the odd occipital lobe and of about the same size as the two inflated lateral buccal lobes, which are separated by a small odd nasal lobe.

Cephalis sexlobate, similar to the preceding species, but with five divergent and curved cylindrical tubes, which correspond to the five spines of Stephanium; an apical tube on the apex of the occipital lobe, a caudal tube on its base, a sternal tube between the two frontal lobes, and two paired pectoral tubes between the latter and the lateral buccal lobes. Pores small and scarce.

Family LVIII. Pylobotryida, Haeckel (sensu emendato).

Pylobotryida, Haeckel, 1881, Prodromus, p. 440.

Definition.—Botryodea trithalamia, the shell of which is composed of a lobate cephalis, a thorax, and an abdomen.

The family Pylobotryida comprises those Botryodea in which the shell exhibits two parallel transverse annular constrictions, and is divided by these into three successive joints, corresponding to the cephalis, the thorax, and the abdomen of the Tricyrtida. As in the latter, the abdomen is here also a later production, arising from the terminal mouth of the thorax; therefore the Pylobotryida must be derived phylogenetically from the Lithobotryida.

Two genera of Pylobotryida were incompletely described in 1860 by Ehrenberg, Botryocyrtis and Botryocampe. We retain them here, with a stricter definition, however. Two other genera were added in my Prodromus—Pylobotrys and Phormobotrys. {1120}The small number of species here enumerated may be easily increased, since numerous forms, belonging probably to this family, are not sufficiently known. Their study is, however, very difficult and requires accurate examination of the tiny shells from different sides.

The four genera of Pylobotryida, here described, represent two different subfamilies. The terminal mouth of the abdomen remains open in the Botryocyrtida, whilst it becomes closed by a lattice-plate in the Botryocampida. There are in both groups shells with and without porous tubes; the number of these tubes, and also the number and disposition of the lobes in the cephalis, exhibits remarkable differences in the different species of those genera, and may in future serve for their division into a greater number of genera.

Synopsis of the Genera of Pylobotryida.

Genus 492. Botryocyrtis,^[109] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 829.

Definition.—Pylobotryida without tubes on the cephalis, and with the mouth of the abdomen open.

The genus Botryocyrtis, founded by Ehrenberg upon two Indian species, is the simplest among the Pylobotryida. It may have been derived from Botryopyle by the development of an abdomen (or a third shell-joint), the mouth of which remains open.

Botryocyrtis serpentis, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 287, Taf. x. fig. 21.

Cephalis quadrilobate; the odd frontal and the two paired buccal lobes subspherical, about half as large as the odd occipital lobe. Thorax inflated, about as long as the cephalis and half as long as the ovate abdomen. Mouth of the latter constricted, of half the breadth.

Cephalis quadrilobate; the odd frontal and the two paired buccal lobes hemispherical, about half as large as the helmet-shaped occipital lobe. Thorax cylindrical, of equal length and breadth, one and a half times as broad as the cephalis and as the cylindrical abdomen. Pores rather large, irregular, roundish.

Cephalis quinquelobate; the odd frontal and the two paired buccal lobes ovate, about half as large as the two helmet-shaped paired occipital lobes (?). Thorax campanulate, twice as broad and long as the cephalis and as the truncate cylindrical abdomen.

Botryocyrtis quinaria, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 287, Taf. x. fig. 16.

Cephalis quinquelobate; the odd occipital lobe ovate, twice as large as each of the other four subspherical lobes, the two anterior (or frontal) of which are somewhat smaller than the two posterior (or buccal). Thorax campanulate, somewhat larger than the truncate abdomen. Pores rather large, irregular.

Genus 493. Pylobotrys,^[110] Haeckel, 1881, Prodromus, p. 440.

Definition.—Pylobotryida with tubes on the cephalis, and with the mouth of the abdomen open.

The genus Pylobotrys differs from the closely allied Acrobotrys, its ancestral form, in the development of an abdomen or a third shell-joint, the basal mouth of which remains open.

Cephalis multilobate, with a single curved and descending tube on the base of its anterior part (sternal tube). Occipital half of the cephalis divided into three large odd lobes (the largest {1122}the apical); facial half divided into three to five lobes, an odd frontal and one or two lateral pairs of small buccal lobes. Thorax truncate conical, about as large as the cephalis and larger than the truncate abdomen. Pores regular circular.

Cephalis trilobate, with three ovate lobes in the sagittal plane, of nearly equal size, and two divergent cylindrical tubes conical at the base. An ascending apical tube on the apex of the occipital lobe and a descending sternal tube on the base of the frontal lobe. The middle lobe between the former distinctly exhibits in the apical view (fig. 20) the collar septum with the four cortinar pores. Thorax campanulate, larger than the cephalis and the truncate abdomen.

Cephalis multilobate, with four divergent cylindrical tubes, which are cylindrical, obliquely truncate at the mouth, and correspond in position to the four typical spines of Cortina; an ascending apical tube and three descending basal tubes (an odd caudal and two paired pectoral). The helmet-shaped occipital lobe is about as large as the frontal half of the cephalis, which is divided into three pairs of smaller pyriform lobes. Thorax subspherical, about as large as the cephalis and half as large as the inflated abdomen. Pores very scarce and small.

Genus 494. Botryocampe,^[111] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 829.

Definition.—Pylobotryida without tubes on the cephalis, and with the mouth of the abdomen closed.

The genus Botryocampe may be derived from Botryocyrtis by development of a basal lattice-plate, closing the terminal mouth of the abdomen. It is at the same time closely allied to the Tricyrtid Theocapsa, and may be perhaps derived from this by lobation of the cephalis.

Botryocampe inflata, Ehrenberg, 1861, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 296; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, p. 285, Taf. ii. fig. 4.

Botryocampe inflata, Haeckel, 1862, Monogr. d. Radiol., p. 345.

Lithobotrys inflata, Bailey, 1856, Amer. Journ. Sci. and Arts, vol. xxii. p. 1, pl. i. fig. 15.

Cephalis trilobate, inflated, of about the same breadth and length as the tun-shaped thorax and the hemispherical abdomen. Frontal lobes of the cephalis ovate, a little smaller than the ovate odd occipital lobe. Pores numerous and small.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, Stations 267 to 274, 241, 354, &c., surface, and in various depths.

Cephalis trilobate, half as long as the campanulate thorax, and one-third as long as the ovate abdomen. Frontal lobes subspherical, scarcely half as long as the helmet-shaped occipital lobe. Pores very small and scarce.

Lithobotrys galea, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 83.

Lithocorythium galea, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 29, a, b.

Lithocorythium galea, Haeckel, 1862, Monogr. d. Radiol., p. 330.

Cephalis quinquelobate, about as large as the ovate thorax, and twice as large as the hemispherical abdomen (which is identical with the "crista obtusa finis anterioris" of Ehrenberg). Occipital lobe helmet-shaped, about twice as long as the two pairs of lateral lobes (the superior frontal and the inferior buccal lobes).

Cephalis quinquelobate, half as large as the campanulate thorax and the subspherical abdomen. Occipital lobe ovate, one and a half times as long as the two ovate frontal lobes, and three times as long as the two subspherical buccal lobes. Collar septum with six distinct cortinar pores (two anterior jugular, two middle cardinal and two posterior cervical, fig. 23).

Cephalis multilobate, about as long and half as broad as the irregularly campanulate thorax, which is half as long as the subspherical large abdomen. Occipital lobe of the cephalis helmet-shaped, larger than its uviform frontal part, which is divided into six to eight small subspherical lobes. In the interior of the thorax and abdomen irregularly branched rods are visible, which divide their inner space into compartments or incomplete chambers. Pores large, regular, circular, hexagonally framed.

Genus 495. Phormobotrys,^[112] Haeckel, 1881, Prodromus, p. 440.

Definition.—Pylobotryida with tubes on the cephalis, and with the mouth of the abdomen closed.

The genus Phormobotrys differs from the similar and closely allied Pylobotrys in the development of a basal lattice-plate closing the terminal mouth of the thorax, and corresponds therefore to Lithobotrys among the Lithobotryida. As in the latter and in Cannobotrys, &c., so here in Phormobotrys, different subgenera may be distinguished, according to the different number and disposition of the radial tubes which become developed from the lobate cephalis.

Cephalis trilobate, with a single apical tube, which is only one-third as long, spindle-shaped, pointed, with frontal opening. Frontal lobes ovate, two-thirds as long as the helmet-shaped occipital lobe. Internal frontal septum of the cephalis with four large pores. Thorax cylindrical, twice as long as the hemispherical abdomen. Pores small and numerous, irregular, roundish.

Cephalis quinquelobate, with a single conical apical tube of the same length, which has an obliquely truncate frontal opening. Odd frontal and paired buccal lobes smaller than the sternal and the occipital lobe. Internal frontal septum with six large pores. Thorax inflated, a little larger than the subspherical abdomen. Pores subregular, circular.

Botryocampe hexathalamia, Haeckel, 1862, Monogr. d. Radiol., p. 344, Taf. xii. fig. 10.

Cephalis sexlobate, with a single apical horn, which is solid, vertical, cylindrical, pointed, only one-third as long. Frontal lobes subcylindrical, nearly as long as the kidney-shaped occipital lobe, three to four times as long as the small buccal lobes and the odd sternal lobe. Thorax tun-shaped, smaller than the cephalis, larger than the hemispherical abdomen. Pores numerous, subregular, circular.

Cephalis trilobate, of about the same breadth and length as the campanulate thorax, which is three times as long as the flat cap-shaped abdomen. The middle (or central) lobe of the cephalis is simple, nearly cubical, and smaller than the ovate occipital and frontal lobe. The two latter are prolonged into two slender cylindrical divergent tubes. Pores small and very numerous.

Cephalis multilobate, of the same length and breadth as the subspherical thorax, and half as long as the ovate abdomen. Occipital lobe helmet-shaped, about as large as the frontal half of the cephalis, which is divided into six to eight lobes (two odd and two or three pairs of lateral lobes). Four cylindrical tubes corresponding to the four typical spines of Cortina, an ascending apical and three descending basal tubes (a posterior caudal and two anterior pectoral).

Suborder III. CYRTOIDEA, Haeckel, 1862.

Cyrtida, Haeckel, 1862, Monogr. d. Radiol., pp. 272, 280.

Cyrtoidea vel Cyrtida, Haeckel, 1881, Prodromus, pp. 425-439.

Polycystina solitaria, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, pp. 53, 54.

Monodictya nassellaria, Ehrenberg, 1875, Abhandl. d. k. preuss. Akad. d. Wiss. Berlin, pp. 156, 157.

Definition.—Nassellaria with a complete lattice-shell, exhibiting a simple or reduced cephalis, which is neither bilocular nor lobate, without sagittal constriction.

The order Cyrtoidea, described by me in 1862 as the family Cyrtida, is by far the largest of all the main groups of Radiolaria, and remarkable from the extraordinary variety of forms and the number of species. In the following system more than eleven hundred species are described, comprising about one-fourth of the number of species in the whole class of Radiolaria. This astonishing variety, however, is not effected by development of a large number of different types, but by an extraordinary variability within certain restricted boundaries, similar to what is seen among insects and birds. The number of genera, therefore, is comparatively small, and they may all be disposed into four families only, which in my Monograph (1862, p. 280) were distinguished as Monocyrtida, Dicyrtida, Tricyrtida and Stichocyrtida. If we divide these four groups in the following pages into twelve families and twenty-four subfamilies, we are guided by practical considerations only, hoping thereby to give a better survey of the difficult labyrinth of Cyrtoidean morphology.

The Cyrtoidea are characterised by this wonderful richness of specific forms not only in the present seas, but also for millions of years in the former ages of our globe. The majority of all the fossil Radiolaria which are now known belong to this group, and many species of it are so common that great rocks are formed by their union. The fact was first observed by Ehrenberg, who in his first system of Polycystina (1847, loc. cit., p. 54) enumerated forty-four genera and two hundred and eighty-two species; the Cyrtoidea, his Polycystina solitaria, form the preponderant majority of the whole class, viz., twenty-five genera and one hundred and ninety-three species.

In this first system (of 1847), as well as in the last systematic table of Ehrenberg (of 1875, loc. cit.), the Cyrtida as "Polycystina solitaria" are opposed to all other Radiolaria, as "Polycystina composita." The former bear the definition "Testæ siliceæ spatio interno ample pervio, aut passim levius transverse constricto"; the latter, however, "Testæ siliceæ spatio interno celluloso aut strictura longitudinali constricto." In reality these definitions are insufficient, and the conclusions which Ehrenberg derived {1127}from the organisation of the Polycystina solitaria and composita, were quite erroneous. So also are the definitions of the three families into which he divided the Polycystina solitaria, afterwards (in 1875) called by him "Monodictya nassellaria." These three families were the Halicalyptrina, Lithochytrina and Eucyrtidina. With these were also united the three genera of Botryodea known to Ehrenberg (Lithobotrys, Botryocampe, Botryocyrtis). We entirely separate these here from the true Cyrtida, on account of their lobate or multilocular cephalis.

Whilst Ehrenberg only knew the skeleton of the Polycystina solitaria, the first observations of living Cyrtida were published by Johannes Müller, 1858, in his fundamental treatise. He gave the first description and figures of the central capsule of this group, with the characteristic lobes developed from its basal part; and of the pseudopodia radiating on all sides (loc. cit., Taf. vi.). The forms described by him were all Mediterranean, one Dicyrtid (Lithomelissa mediterranea), two Tricyrtids (Eucyrtidium zancleum and Pterocanium charybdeum), and one Stichocyrtid (Lithocampe tropeziana).

In my monograph (1862, p. 272-341) I gave a detailed description of all known and some new Cyrtida, and characterised this family by the fundamental monaxonial form of the shell, with two different poles (an upper apical and a lower basal pole), and by the unipolar growth, beginning from the apical pole. I pointed out also the peculiar structure of the monaxonial central capsule. At that time I divided the Cyrtida into five subfamilies, in which, however, the Spyroidea (= Zygocyrtida), and the Botryodea (= Polycyrtida) were united with the true Cyrtoidea (Monocyrtida, Dicyrtida, Stichocyrtida).

The astonishing number of new and interesting forms of Cyrtida which I found in the rich collection of the Challenger (beginning from 1876), and mainly in the Radiolarian ooze of the Central Pacific (Stations 263 to 274), enabled me to give in my Prodromus, in 1881, a greatly enlarged and amended system of this important group. I separated there the Spyroidea (= Zygocyrtida), and the Botryodea (= Polycyrtida) from the true Cyrtoidea by restricted definition, pointing out the essential differences in the structure of the cephalis in these groups of Cyrtellaria. The latter name, as here used, is therefore identical with the "Cyrtida" of my Monograph. In the Prodromus I divided the true Cyrtida (p. 426) into five subfamilies and thirty tribes, corresponding to the differences in the number of the shell-joints and of the radial apophyses, and in the shape of the closed or open mouth. These groups are here retained, but reduced to four families and twenty-four subfamilies, since the Tetracyrtida are better united with the Stichocyrtida (compare below).

Richard Hertwig in his work Organismus der Radiolarien (1879, pp. 74 to 86) gave the first accurate description of the finer structure of the central capsule of the Cyrtida, and pointed out their character as true Monopylea, with porochora and {1128}podoconus, and the peculiar shape of its nucleus. He also published excellent figures of some interesting new species.

O. Bütschli, 1882, in his valuable paper entitled: "Beiträge zur Kentniss der Radiolarien-Skelette, insbesondere der der Cyrtida" (Zeitschr. für wiss. Zool., vol. xxxvi. p. 485) made an attempt at a natural classification of the Cyrtida, which he derived from the Spyroidea or Zygocyrtida. As already mentioned above, we cannot accept this essay as the foundation of a true natural system, since the affinities of the Cyrtellaria (and of the Nassellaria as a whole) are far more complicated and difficult than Bütschli supposed. His views were supported by accurate observations only on the structure of the fossil Cyrtoidea of Barbados; these, however, represent the minority only of the genera, and many interesting and important forms (mainly of true "Monocyrtida") remained unknown to Bütschli. A great part, however, of his observations are very useful, and his remarks on comparative morphology are very suggestive.

The Cyrtoidea may be divided into families and subfamilies according to three different principles, viz., (1) the number of joints into which the shell is divided by transverse strictures; (2) the number of radial apophyses which arise from the shell; (3) the shape of the basal mouth, which is either open or closed by a lattice-plate. At present every attempt of classification in this large group must be more or less artificial, since the affinities of the numerous smaller and larger groups are extremely complicated, and the ontogeny, the only sure guide in this phylogenetical labyrinth, is perfectly unknown. It seems therefore the most convenient to employ for our artificial classification, first, the number of shell-joints, second, the radial structure, and third, the shape of the mouth.

A. The number of joints into which the shell is divided by transverse constrictions, serves here for the distinction of four primary groups or suborders of the Cyrtoidea, viz., (1) Monocyrtida with one joint; (2) Dicyrtida with two joints; (3) Tricyrtida with three joints; and (4) Stichocyrtida with four or more joints. In my Prodromus (1881, p. 426) I divided the latter group into Tetracyrtida (with four joints), and Stichocyrtida (with five or more joints); but these two groups may be united, since the fourth and all the succeeding joints are of rather indifferent shape and of little morphological value. The three first joints, however, are usually very different and possess a high morphological importance, so that we distinguish the first joint as cephalis, the second as thorax, and the third as abdomen. The uppermost transverse constriction, which separates the two first joints, cephalis and thorax, is the collar stricture and is usually caused by an internal fenestrated septum, the cortinar septum. The second constriction, which separates the second and third joints (thorax and abdomen) is called the lumbar constriction. The following constrictions (in the Stichocyrtida) are indifferent and of little morphological interest, and require therefore no peculiar designation.

B. The radial structure, indicated by radial apophyses arising from the shell, offers three principal differences, according to which the whole group of Cyrtoidea may be divided into three large groups or sections, viz., (1) Pilocyrtida, or Cyrtoidea triradiata, with three radial apophyses; (2) Astrocyrtida, or Cyrtoidea multiradiata, with numerous radial apophyses (four to nine or more); and (3) Corocyrtida, or Cyrtoidea eradiata, without external radial apophyses. The majority of Cyrtoidea are Pilocyrtida, with three radial apophyses, which are probably homologous to the three primary feet of the Plectoidea and of Cortina (therefore "cortinar feet"). The Astrocyrtida, or the Cyrtoidea with a variable number of radial apophyses (at least four to six) may be derived from the Pilocyrtida by interpolation of secondary or interradial apophyses between the three primary or perradial apophyses. The Corocyrtida, however, or the Cyrtoidea without external radial apophyses, may have originated by reduction and loss of the latter, either from the Pilocyrtida or from the Astrocyrtida.

C. The shape of the basal mouth in the Cyrtoidea exhibits two essential differences only, viz., (1) the terminal mouth of the shell is a simple wide opening in the Stomocyrtida, or (2) the terminal mouth is closed by a lattice-plate, in the Clistocyrtida. As these two different cases occur in all the twelve families, which we have distinguished according to the differences in the number of joints and in the radial structure, we get altogether twenty-four subfamilies which are synoptically arranged in the following table:—

Synopsis of the four sections, twelve families and twenty-four subfamilies of CYRTOIDEA.	PILOCYRTIDA. Cyrtoidea triradiata. (Three radial apophyses.)	ASTROCYRTIDA. Cyrtoidea multiradiata. (Four to nine or more apophyses.)	COROCYRTIDA. Cyrtoidea eradiata. (No radial apophyses.)
Mouth of the shell.	Aperta.	Clausa.	Aperta.	Clausa.	Aperta.	Clausa.
MONOCYRTIDA. (Cyrtoidea monothalamia).	Tripocalpida.	Phænocalpida.	Cyrtocalpida.
Archipilida.	Archiperida.	Archiphormida.	Archiphænida.	Archicorida.	Archicapsida.
DICYRTIDA. (Cyrtoidea dithalamia).	Tripocyrtida.	Anthocyrtida.	Sethocyrtida.
Sethopilida.	Sethoperida.	Sethophormida.	Sethophænida.	Sethocorida.	Sethocapsida.
TRICYRTIDA. (Cyrtoidea trithalamia).	Podocyrtida.	Phormocyrtida.	Theocyrtida.
Theopilida.	Theoperida.	Theophormida.	Theophænida.	Theocorida.	Theocapsida.
STICHOCYRTIDA. (Cyrtoidea polythalamia).	Podocampida.	Phormocampida.	Lithocampida.
Stichopilida.	Stichoperida.	Stichophormida.	Stichophænida.	Stichocorida.	Stichocapsida.

Synopsis of the four sections, twelve families and twenty-four subfamilies of CYRTOIDEA.	PILOCYRTIDA. Cyrtoidea triradiata. (Three radial apophyses.)
Mouth of the shell.	Aperta.	Clausa.
MONOCYRTIDA. (Cyrtoidea monothalamia).	Tripocalpida.
Archipilida.	Archiperida.
DICYRTIDA. (Cyrtoidea dithalamia).	Tripocyrtida.
Sethopilida.	Sethoperida.
TRICYRTIDA. (Cyrtoidea trithalamia).	Podocyrtida.
Theopilida.	Theoperida.
STICHOCYRTIDA. (Cyrtoidea polythalamia).	Podocampida.
Stichopilida.	Stichoperida.
	ASTROCYRTIDA. Cyrtoidea multiradiata. (Four to nine or more apophyses.)
Mouth of the shell.	Aperta.	Clausa.
MONOCYRTIDA. (Cyrtoidea monothalamia).	Phænocalpida.
Archiphormida.	Archiphænida.
DICYRTIDA. (Cyrtoidea dithalamia).	Anthocyrtida.
Sethophormida.	Sethophænida.
TRICYRTIDA. (Cyrtoidea trithalamia).	Phormocyrtida.
Theophormida.	Theophænida.
STICHOCYRTIDA. (Cyrtoidea polythalamia).	Phormocampida.
Stichophormida.	Stichophænida.
	COROCYRTIDA. Cyrtoidea eradiata. (No radial apophyses.)
Mouth of the shell.	Aperta.	Clausa.
MONOCYRTIDA. (Cyrtoidea monothalamia).	Cyrtocalpida.
Archicorida.	Archicapsida.
DICYRTIDA. (Cyrtoidea dithalamia).	Sethocyrtida.
Sethocorida.	Sethocapsida.
TRICYRTIDA. (Cyrtoidea trithalamia).	Theocyrtida.
Theocorida.	Theocapsida.
STICHOCYRTIDA. (Cyrtoidea polythalamia).	Lithocampida.
Stichocorida.	Stichocapsida.

The cephalis, or the first shell-joint of the Cyrtoidea, is in the majority homologous with the cephalis of the Spyroidea, from which it differs in the reduction of the sagittal ring and the absence of the corresponding sagittal constriction; its cavity is therefore simple, not bilocular. Its homology with the original cephalis of the Spyroidea cannot be doubted, when its base exhibits the typical basal pores of the Semantida. But in many cases these are wanting, and in a great number of Cyrtoidea (mainly of Monocyrtida) there is more or less evidence that the original cephalis is lost, and that the real first joint is the thorax, the original second joint. At present it is quite impossible to distinguish between the former and the latter shells, and therefore in the following descriptions the first joint is always named cephalis and the second thorax. In future, when the affinities of the Cyrtoidea become better known, it will be necessary to distinguish the "Archicephalis," or true cephalis of all Spyroidea and of the majority of Cyrtoidea, from the "Pseudocephalis" or the false cephalis of the minority (e.g., of many Monocyrtida aperta, Archipilida, Archiphormida, Archicorida, &c.).

The thorax, or the second shell-joint of the Cyrtoidea, is in the majority homologous with the thorax of the Phormospyrida and Androspyrida, and therefore developed by apophyses, which arise from the base of the cephalis and become united by transverse branches forming a lattice-plate. Its size is generally in inverse proportion to that of the cephalis. The more the cephalis becomes reduced, the more the thorax is developed. Its form is very variable, usually three-sided pyramidal or prismatic in the triradiate, polyhedral in the multiradiate, and conical or cylindrical in the eradiate Cyrtoidea. Its terminal mouth is either a simple wide opening, or closed by a lattice-plate. In the majority of Cyrtoidea the thorax is separated from the cephalis not only by the external collar constriction, but also by the internal cortinar septum, a horizontal lattice-plate which exhibits the typical basal pores of the Semantida (usually two smaller jugular and two larger cardinal pores). But this septum is often reduced or perfectly lost, and then the external collar constriction alone indicates the separation of the cephalis and the thorax.

The abdomen, or the third shell-joint of the Cyrtoidea, absent in the Monocyrtida and Dicyrtida (as also in all Spyroidea), occurs constantly in all Tricyrtida and Stichocyrtida. It is a simple large chamber in the Tricyrtida, but forms an annulated body, composed of a variable number of successive joints, in the Stichocyrtida. The constrictions between these joints, and also the lumbar constriction, between abdomen and thorax, are usually provided with a lattice-girdle, projecting into the cavity of the shell, like a diaphragm. Usually this horizontal girdle bears only a single circle of pores, rarely two or more. In many Cyrtoidea it is replaced by a solid horizontal ring of silex, and often it is wanting. It originates by the insertion of the following shell-joint, which takes place not on the terminal mouth of the preceding joint, but somewhat above it.

The annular joints of the Stichocyrtida succeeding the third joint, and very variable in number, may be regarded either as a series of new postabdominal chambers, succeeding the true abdomen, or as secondary joints of the annulated abdomen itself. The latter view may be sustained by the fact that these joints are usually of an indifferent shape, and do not possess the characteristic features which we find in the first three joints, the abdomen, the thorax and the cephalis.

The lattice-work of the shell exhibits in the Cyrtoidea an extraordinary variety, similar to that of the Sphæroidea; it serves in the first place for the distinction of species. The three first joints of the shell are often distinguished by the different character of the lattice-work. The cephalis has usually very small and simple pores. The lattice-work of the thorax is often characterised by radial structures. The pores of the abdomen are usually very numerous and regular. The numerous joints in the annulated abdomen of the Stichocyrtida commonly exhibit little variety.

The closure of the mouth, effected by a convex or horizontal terminal lattice-plate, has a different signification in the Monocyrtida and in the jointed Cyrtoidea. In the Monocyrtida clausa this closing plate is the original cortinar plate or the basal plate of the cephalis. In the jointed Cyrtoidea, however, the lattice-plate which closes the terminal mouth of the thorax or of the abdomen (of the last annular joint in the Stichocyrtida), is produced by central union of the convergent edges, which grow centripetally from the margin of the mouth of the last joint towards its centre.

The radial apophyses arising from the shell of the Cyrtoidea may probably be always derived from that tripodal structure which is found in all Plectoidea, in Cortina and Cortiniscus among the Stephoidea, and in the majority of Spyroidea. Therefore the prototype of this radial structure would be Plagoniscus and Cortina, with four radial spines united in a common point, the cortinar centrum; an ascending apical horn and three descending basal feet. The odd posterior or caudal foot is usually similar in shape to the two paired anterior or pectoral feet, but may be distinguished from these latter by its relation to the apical horn. Very frequently an internal vertical free columella arises in the cephalis, or instead of it an ascending rib in the dorsal wall of the cephalis, which connects the base of the apical horn with the origin of the caudal foot. This is probably the remaining part of the sagittal ring. More rarely also a part of the ventral rod of the latter is preserved, or on the anterior pole of the basal rod of the cephalis an ascending procolumella arises which is inserted on the frontal face of the cephalis, and sometimes prolonged into a nasal horn (the rod, C, of Bütschli). These two odd horns, the posterior apical horn and the anterior nasal horn, are usually different and divergent. In some genera a variable number of accessory radial horns is developed on the convex face of the cephalis. In many hornless genera the free apical horn is lost, but not unfrequently the columella is preserved which connects the caudal foot with that point of the cephalis, in which formerly the apical horn was inserted.

The three primary radial beams, corresponding to the three basal feet of Plectaniscus and Cortina, exhibit in the Cyrtoidea the greatest variety in form and size, and chiefly in their relation to the shell, the latter serving mainly for the distinction of genera. Originally these three cortinar beams arise from the basal plate of the cephalis, the odd caudal foot appearing as a prolongation of the basal rod of that plate, and the paired pectoral feet as prolongations of its coracal rods (between the jugular and cardinal pores). The lattice-work of the thorax is developed usually between the three cortinar feet, more rarely inside or outside of them. Therefore the three beams appear commonly as three divergent ribs in the wall of the thorax, and continue over its basal mouth as three free terminal feet. With the increasing length of the shell and the number of its joints the three radial ribs are also prolonged, and their free distal ends may be prominent at very different points, either as three lateral wings or as three terminal feet. These are either solid spines or lattice-plates, sometimes more or less ramified.

The three radial apophyses are prevalent in the majority of the Cyrtoidea, which we call "Pilocyrtida" (or Cyrtoidea triradiata). Their number increases in the Astrocyrtida (or Cyrtoidea multiradiata). The most frequent cases of multiplication are here caused by the development of six or nine radial apophyses; these may be enclosed ribs, or lateral wings, or terminal feet. In the sexradial Cyrtoidea there are three secondary or interradial apophyses interpolated between the three primary or perradial; in the nine-radial Cyrtoidea, however, there are six adradial apophyses interpolated.

A third and last great group is formed by the Corocyrtida or Cyrtoidea eradiata. These exhibit no radial apophyses, neither enclosed ribs, nor free lateral wings, nor terminal feet. But in a great number of them internal traces of an original triradiate structure are visible, mainly in the cortinar septum between cephalis and thorax; this often exhibits three or four, and sometimes six cortinar or collar pores, of the same typical shape as in the triradial Spyroidea. Sometimes even an internal columella with three radial branches is preserved, as in Axocorys. It is therefore very probable that a great part of these Cyrtoidea eradiata (if not all) may be derived from triradiate or multiradiate ancestral forms, by reduction and loss of the radial apophyses. In another part of this group, mainly in the Monocyrtida eradiata (Cyrtocalpida) it is possible, or even probable, that their eradiate shell has originated independently from Nassellida, and that they have no true relation to radial Cyrtoidea.

The Central Capsule of the Cyrtoidea, first observed by J. Müller (1858), and more fully described in my Monograph (1862), was very accurately examined by Richard Hertwig (1879). His observations were confirmed by numerous new forms, which I was able to examine in well-preserved preparations of the Challenger. The central capsule, according to these, exhibits the same typical shape, which is characteristic of all Monopylea (with porochora and podoconus), and may be derived with the latter from the common ancestral forms, Cystidium and Nassella (= the skeletonless Nassellida). In {1133}the majority, however, of Cyrtoidea, the capsule develops on its basal face a number of depending lobes, as were also found in some Spyroidea (and probably also Botryodea). In this respect we may distinguish two main forms of the capsule in the Cyrtellaria, viz., the primary simple, not lobate form, and the secondary lobate form. The central capsule is originally always enclosed in the cephalis, and has there a simple, subspherical, ellipsoidal or ovate form. As soon as their growth increases, and the enclosing cephalis becomes too narrow, it sends out prolongations in the form of basal lobes, which depend from its base, and proceed through the pores of the basal lattice of the cephalis, or the cortinar pores. In the great majority of Cyrtoidea in which the capsule was observed, either three or four such lobes were seen (already described by J. Müller). Of course this number depends upon the number of cortinar pores, which is either three or four; therefore in the Cyrtoidea with three pores in the cortinar plate, we find three lobes of the central capsule (an odd posterior and two paired anterior); in the Cyrtoidea, however, with four pores in the cortinar plate (the majority) we find four lobes of the central capsule (two smaller anterior jugular and two larger posterior cardinal lobes). Usually each lobe is ovate or pear-shaped and encloses a large oil-globule, and often also an apophysis of the cell-nucleus.

Section I. MONOCYRTIDA, Haeckel, 1862, Monogr. d. Radiol., pp. 280, 281.

Definition.—Cyrtoidea monothalamia, with simple, not jointed shell (or cephalis), without transverse constrictions.

Synopsis of the three Families and six Subfamilies of Monocyrtida.

Family LIX. Tripocalpida, n. fam.

Archipilida et Archiperida, Haeckel, 1881, Prodromus, pp. 427, 429.

Definition.—Monocyrtida triradiata. (Cyrtoidea with a simple, not jointed shell, representing a simple cephalis, with three radial apophyses.)

The family Tripocalpida, composed of the Archipilida and Archiperida of my Prodromus, comprises those Cyrtoidea in which the lattice-shell is quite simple, without transverse constriction, and bears three radial apophyses. The two subfamilies differ in the shape of the basal mouth, which in the Archipilida is a simple wide opening, in the Archiperida closed by a lattice-plate; the former are here divided into eight, the latter into seven different genera.

Only three species of this family were hitherto described, all three belonging to the Archipilida, viz., (1) Tripocalpis galea (fossil in Barbados, figured by Ehrenberg, 1875, as Halicalyptra galea), (2) Tripodiscium campanula (fossil in Sicily, figured by Stöhr, 1880, as Carpocanium); and (3) Tridictyopus elegans, of which Richard Hertwig gave an excellent description in 1879, with an accurate figure of the central capsule. All the other species of the family (seventy) are new.

The shell in the majority of Tripocalpida is ovate or campanulate, sometimes conical or three-sided pyramidal. Three radial apophyses are constantly distinct, either three lateral wings or three terminal feet; these are usually solid spines, rarely lattice-plates. The top of the shell usually bears an apical horn, rarely two or more horns; often the horn is wanting. The lattice-work of the shell is very various in the different species, and often of a remarkable structure (Pl. 51, figs. 6-8; Pl. 98, figs. 4-8). The cavity of the shell is in all Archipilida, and in a part of the Archiperida (Peridium, Archipera, Archibursa) quite simple. In the other part of the Archiperida, however, constituting the peculiar group of Euscenida (genera 504-507), a vertical columella arises in the centre of the basal plate, and is prolonged upwards in the apical horn; this columella is either simple (Euscenium, Archiscenium) or branched (Cladoscenium, Pteroscenium); in the latter case the ascending branches are disposed in triradiate verticils and are inserted on the inner face of the shell (compare Pl. 53, figs. 11-16, and Pl. 98, figs. 1-4).

The phylogenetic origin of the Tripocalpida may be very divergent, and their morphological affinity to the other Nassellaria is a very complicated problem. The Euscenida (genera 504-507) may be derived directly from the Plagonida (Plagoniscus) or Plectanida (Plectaniscus). The Archibursida (genera 508-510) however, manifest a closer affinity to the Tripospyrida, and may be derived from them by reduction of the sagittal ring and constriction. In these two groups of Archiperida the shell may be regarded as a true cephalis. In the Archipilida, however, where the shell has a wide basal opening and the three radial ribs arise originally from the base of the apical horn, the shell itself may correspond to the thorax of the Dicyrtida, and may be derived from these by loss of the cephalis. This is the more probable, as sometimes a small remnant of the reduced cephalis is preserved (Pl. 98, fig. 8). None of these difficult questions can be answered until a much closer morphological knowledge of the Tripocalpida is acquired.

Synopsis of the Genera of Tripocalpida.

Subfamily 1. Archipilida, Haeckel, 1881, Prodromus, p. 427.

Definition.—Tripocalpida with the basal mouth of the shell open (vel Monocyrtida triradiata aperta).

Genus 496. Tripocalpis,^[113] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three lateral ribs prolonged into three terminal feet. Apex with a horn.

The genus Tripocalpis opens the series of Archipilida, or of those Monocyrtida in which the monothalamous shell exhibits a distinct triradial structure, and a simple open mouth, without cortinar lattice. Tripocalpis is probably the most primordial of the Archipilida, and has three lateral ribs, which are prolonged into three free terminal {1136}feet, and connected in the apex of the pyramidal or campanulate shell with the apical horn. It may probably be derived from Dictyophimus by loss of the cephalis. The central capsule is simple, spherical, or ellipsoidal.

Shell three-sided pyramidal, smooth, about as long as broad, with irregular polygonal pores and thin bars. Apical horn stout, three-sided pyramidal, about as long as the shell. From the three edges of its base arise three prominent straight radial ribs, which are prolonged into three large divergent feet, of equal size and the same form as the horn.

Habitat.—Tropical Pacific (Philippine Sea), Station 206, depth 2100 fathoms.

Halicalyptra galea, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. ii. fig. 10.

Shell campanulate, rough, about as long as broad, with irregular roundish pores and thick bars. Apical horn stout, three-sided pyramidal, scarcely one-fourth as long as the shell. Beyond its base there arise three prominent, slightly curved lateral ribs, which are prolonged into three pyramidal, slightly divergent stout feet, somewhat shorter than the shell.

Shell ovate campanulate, one and a half times as long as broad, with regular circular pores, disposed in alternate longitudinal rows. Apical horn three-sided pyramidal, stout, half as long as the shell. In the middle of the shell there arise three wing-like lateral ribs, which are prolonged into three broad, slightly curved, divergent terminal feet.

Shell ovate, nearly twice as long as broad. The three sides of the shell, between the three large ribs, are provided each with nine delicate parallel, longitudinal, slightly curved ribs, alternating with ten longitudinal rows of regular circular pores about as broad as the bars. Apical horn short and broad, three-sided pyramidal; from the three edges of its base there arise three wing-like serrate main ribs, which are prolonged into three short pyramidal terminal feet.

Shell hemispherical, one and a half times as broad as long, with regular, circular, hexagonally framed pores, Apical horn stout, three-sided pyramidal, with three serrate edges. From the base of the latter arise three strongly dentate and curved lateral ribs, with recurved teeth, and these are prolonged into the serrate convex edge of the three basal feet, which are crescentic and twice as long as the shell.

Genus 497. Tripodonium,^[114] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three lateral ribs prolonged into three terminal feet. Apex without horn.

The genus Tripodonium differs from the preceding Tripocalpis, its probable ancestral form, only in the loss of the apical horn (already very small in some forms of the latter). It bears therefore to the latter the same relation that Sethopilium does to Dictyophimus.

Shell campanulate, somewhat broader than high, with regular circular pores, twice as broad as the bars. Three broad lateral wings, lamellar, triangular, are prolonged over the peristome into three short triangular lamellar feet one-fourth as long as the shell.

Shell ovate, one and one-third times as long as broad, with numerous and small circular pores, scarcely as broad as the bars. Three prominent longitudinal ribs, arising in the lower half of the shell-wall, are prolonged into three divergent conical curved feet, about half as long as the shell.

Genus 498. Tripterocalpis,^[115] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three lateral wings and a peristomial corona of numerous terminal feet. Shell ovate, with constricted mouth, without apical horn.

The genus Tripterocalpis is distinguished from the other Archipilida by the remarkable combination of three lateral wings and of numerous (six to nine or more) terminal feet. It may be derived directly from the preceding Tripocalpis by multiplication of the terminal feet. These are sometimes obliquely directed. The central capsule is ellipsoidal or ovate, and fills up the greater part of the shell.

Shell slender, ovate, nearly twice as long as broad. Pores circular, of different sizes and at unequal distances. Along the lower half of the shell there arise three broad triangular lamellar wings. Peristome with twelve conical, nearly parallel and vertical feet, about one-sixth as long as the shell.

Shell ovate, nearly as broad as long. Pores regular, circular, quincuncial, twice as broad as the bars. In the middle of the shell there arise three conical, smooth, divergent wings, about half as long as the shell. Peristome with six short triangular, oblique, convergent feet.

Shell ovate, nearly as broad as long. Pores small and numerous, circular or roundish, partly confluent, double-contoured (fig. 4). In the middle of the shell there arise three very large conical divergent wings, which are longitudinally striped and longer than half the shell. Peristome with nine short triangular, oblique, convergent feet.

Genus 499. Trissopilium,^[116] Haeckel, 1881, Prodromus, p. 427.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three lateral ribs or wings. Mouth smooth, without terminal feet. Apex with a horn.

The genus Trissopilium and the following nearly allied Archipilium differ from the other Archipilida in the absence of terminal feet, the peristome being quite simple, and truncate. But there are three lateral wings, arising either from the apex or from the lateral sides of the monothalamous shell. Trissopilium may perhaps be derived from Lithomelissa by reduction of the cephalis.

Shell in the upper half three-sided pyramidal, in the lower half inversely hemispherical, of equal length and breadth. Pores irregular, roundish, in the upper half larger. From the apex there diverge four equal, straight and stout, three-sided pyramidal spines, one of which is vertically ascending (the horn), the three others obliquely descending (the wings). The distal half of the latter is free, whilst the proximal half forms three ribs, enclosed in the shell-wall. Mouth constricted, half as broad as the shell.

Shell ovate, one and one-third times as long as broad. Pores circular, of different sizes, small and numerous. Apical horn very large, straight, cylindrical, vertical, longer than the shell. Three lateral wings shorter, arising from the middle of the shell, conical, curved, divergent. Mouth truncate, two-thirds as broad as the shell.

Genus 500. Archipilium,^[117] Haeckel, 1881, Prodromus, p. 427.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three lateral ribs or wings. Mouth truncate, without terminal feet. Apex without horn.

The genus Archipilium differs from the nearly allied Trissopilium, its probable ancestral form, in the absence of the apical horn. The three lateral wings of the ovate shell are stout spines. It may also be derived from the similar Sethopilium by reduction and loss of the cephalis.

Shell ovate, smooth, nearly cylindrical, scarcely broader than the truncate, widely open mouth. Pores numerous, irregular, roundish, of very different sizes. Three lateral wings arising from the middle zone, twice as long as the shell, straight, divergent, stout, cylindrical, longitudinally striped.

Shell ovate, smooth, nearly campanulate, of equal length and breadth, one and one-third times as broad as the truncate, slightly constricted mouth. Pores scarce, irregularly formed and {1140}scattered, of very different sizes. Three lateral wings, stout, prismatic, about as long as the shell widely divergent and S-shaped, curved.

Shell ovate, rough, twice as broad as the constricted mouth. Pores small and numerous, subregular, circular, smaller than the bars. Three lateral wings cylindrical, crescentic, in the upper half divergent, in the lower convergent, one and one-half times as long as the shell.

Genus 501. Tripilidium,^[118] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) without lateral ribs, with three simple or branched terminal feet and an apical horn.

The genus Tripilidium differs from Tripodonium in the absence of the three lateral ribs, and may be derived either from this ancestral form, or directly from Tripospyris (by loss of the sagittal ring and constriction); perhaps also from Lychnocanium (by reduction of the cephalis). We distinguish as two subgenera, Tristylocorys (with simple feet) and Tripodocorys (with branched feet).

Subgenus 1. Tristylocorys, Haeckel.

Shell campanulate, rough, about as long as broad. Pores subregular, circular, larger in the middle zone, twice to three times as broad as the bars. Mouth constricted, half as broad as the shell. Apical horn straight and stout, three-sided pyramidal, about as long as the shell. Three feet divergent, slightly S-shaped, curved, somewhat longer the the shell.

Shell hemispherical, smooth, nearly twice as broad as long. Pores large, with thin bars, irregular, roundish, of very different sizes. Mouth wide open. Apical horn conical, half as long as {1141}the shell. Three feet slender cylindrical, widely divergent, curved, nearly twice as long as the shell.

Shell hemispherical, thorny, one and a half times as broad as long. Pores regular, circular, hexagonally framed, as broad as the bars. Mouth slightly constricted. Apical horn stout and short, three-sided pyramidal. Three feet cylindrical, straight, divergent, twice to three times as long as the shell. (Similar to Lychnocanium favosum, Pl. 61, fig. 6, perhaps derived from it by reduction of the cephalis.)

Shell ovate, smooth, one and one half times as long as broad. Pores regular, circular, as broad as the bars. Mouth constricted, half as broad as the shell. Horn short, conical. Three feet conical, curved, convergent, scarcely one-third as long as the shell.

Shell nearly spherical, tuberculate, a little broader than long. Pores regular, circular, as broad as the bars. Mouth constricted, half as broad as the shell. Apical feet and the three divergent feet of equal size and similar form, about as long as the shell, straight, in the basal half smooth, cylindrical, in the distal half club-shaped, dimpled. (Very similar to Tripospyris conifera and Tripospyris eucolpos, Pl. 84, figs. 7 and 4; but the spherical shell exhibits no trace of sagittal ring or constriction, and the simple shell-cavity has a wide open mouth, and is not closed by a basal plate.)

Shell ovate, spinulate and costate, nearly twice as broad as long. Surface with fifteen to twenty prominent longitudinal ribs, which are convergent towards each pole and elegantly denticulate. The deep furrows between them are divided by delicate, parallel, transverse ribs into numerous short and broad dimples (thirty to forty in each furrow); each dimple contains a small pore, like a transverse {1142}fissure. The apex bears a short and stout, three-sided pyramidal horn, the hollow base of which is closed by a small cortinar septum with three collar pores (fig. 8b). This seems to indicate a rudimentary cephalis and the derivation of this species from Lychnocanium (Pl. 61). Peristome constricted, only one-fourth as broad as the shell, with three short, conical, nearly vertical feet. The central capsule (fig. 8a) in the specimen examined was well preserved, hemispherical, not lobate, and filled up the upper half of the shell-cavity (beyond the rudiment of the cortinar septum).

Shell elongate, smooth, nearly cylindrical, in the upper third conical. Pores small and numerous, regular, circular, half as broad as the bars, disposed in about thirty longitudinal alternating rows. Peristome scarcely constricted. The apical horn and the three parallel feet are of equal size and similar form, straight, conical, one-sixth as long as the shell.

Subgenus 2. Tripodocorys, Haeckel, 1881, Prodromus, p. 428.

Shell hemispherical, nearly twice as broad as long, smooth. Pores irregular, roundish, twice to four times as broad as the bars. Mouth wide open. Apical horn spindle-shaped, half as long as the shell. Three feet cylindrical, nearly straight and parallel, as long as the shell, forked at the distal end. (Exhibits an external similarity to Tripospyris semantis, Pl. 84, fig. 2, but has no trace of sagittal ring and constriction, and the simple shell-cavity has a wide open mouth.)

Shell campanulate, rough, about as long as broad. Pores subregular, circular, as broad as the bars. Mouth slightly constricted. Apical horn and three divergent feet of nearly equal size and form, three-sided prismatic, straight and stout, irregularly dentate and branched, somewhat longer than the shell.

Genus 502. Tripodiscium,^[119] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) without lateral ribs and apical horn, with three simple or branched terminal feet.

The genus Tripodiscium may be derived either from the preceding Tripilidium by loss of the apical horn, or from the nearly related Tristylospyris by loss of the sagittal ring and constriction. Some forms of the latter genus can scarcely be distinguished from similar species of the former.

Subgenus 1. Tripodiscinus, Haeckel.

Shell subspherical, with regular, circular pores, twice as broad as the bars. Mouth constricted, half as broad as the shell, with three short spindle-shaped feet, which are nearly parallel and vertical, half as long as the shell. (Similar to Tristylospyris scaphipes, Pl. 84, fig. 13, but without sagittal ring and constriction.)

Shell ovate, rough, nearly as broad as long. Pores regular circular, double-contoured, twice as broad as the bars. Mouth constricted, one-third as broad as the shell, with three convergent short triangular feet.

Shell ovate, smooth, one and a half times as long as broad. Pores irregular roundish, of different sizes. Mouth constricted, two-thirds as broad as the shell, with three divergent, straight club-shaped feet, nearly as long as the shell.

Carpocanium campanula, Stöhr, 1880, Palæontogr., vol. xxvi. p. 96, Taf. iii. fig. 9.

Shell campanulate or subspherical, smooth, about as long as broad. Pores small, regular circular, as broad as the bars. Mouth constricted, about half as broad as the shell, with three short conical descending feet.

Subgenus 2. Tripodisculus, Haeckel.

Shell ovate, rough, nearly as broad as long. Pores subregular, circular, twice as broad as the bars. Mouth constricted, two-thirds as broad as the shell, with three divergent parallel and vertical feet, which are as long as the shell, and forked at the distal end.

Shell ovate, tuberculate, nearly as broad as long. Pores irregular, roundish, of very different sizes. Mouth constricted, half as broad as the shell, with three large, divergent, irregularly branched feet, nearly twice as long as the shell. (Similar to Tristylospyris ramosa, Pl. 52, fig. 23, but without sagittal ring and constriction.)

Shell subspherical, rough, with circular pores of different sizes. Mouth constricted, circular, simple, two-thirds as broad as the shell, with three large divergent feet, which are three-sided prismatic, irregularly branched, and twice as long as the shell.

Genus 503. Tridictyopus,^[120] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archipilida (vel Monocyrtida triradiata aperta) with three latticed terminal feet. Shell ovate or subconical, with an apical horn.

The genus Tridictyopus differs from the nearly allied Tripilidium in the possession of three large fenestrated shovel-shaped feet, forming direct prolongations of the large conical shell. The lattice work exhibits a peculiar elegant structure recurring in the similar, perhaps nearly related, Cephalospyris (Pl. 83, fig. 10; Pl. 96, fig. 28). The central capsule is large, ellipsoidal or ovate, and fills up the greater part of the shell cavity (compare R. Hertwig, 1879, loc. cit., p. 75).

Shell campanulate, about as long as broad (excluding horn and feet). Pores irregular, polygonal, in the middle part more regular, triangular. Horn short and stout, three-sided pyramidal. Three feet large, triangular, shovel-shaped, about half as long as the shell.

Shell campanulate conical, about one and a half times as long as broad (excluding horn and feet). Pores mostly triangular, disposed in subregular hexagonal figures, which are separated by bands of smaller irregular polygonal pores. Horn short and stout, three-sided pyramidal. Three feet triangular shovel-shaped, convergent, about one-sixth as long as the shell.

Tridictyopus elegans, R. Hertwig, 1879, Organismus d. Radiol., p. 75, Taf. vii. fig. 3, 3a, 3b.

Shell slender, conical, campanulate, about twice as long as broad (excluding horn and feet). Most pores subregular triangular, with some irregular polygonal ones intermingled. The horn in the two observed specimens was broken off, together with the conical apex of the shell. Three feet triangular shovel-shaped, about one-sixth as long as the shell.

Subfamily 2. Archiperida, Haeckel, 1881, p. 429.

Definition.—Tripocalpida with the basal mouth of the shell fenestrated (vel Monocyrtida triradiata clausa).

Genus 504. Euscenium,^[121] n. gen.

Definition.—Archiperida (vel Monocyrtida triradiata clausa) with a free simple internal columella, prolonged into an apical horn. Three basal feet free, without lateral wings.

The genus Euscenium and the three following nearly allied genera form together the remarkable small group of Euscenida, probably one of the oldest and most primitive of all Cyrtoidea, and perhaps the common root of this suborder, arising directly from the Plectoidea. The simple skeleton is composed of four radial beams united in one point (the cortinar centrum). Three beams are directed downwards, and form three divergent basal feet; the fourth beam is directed upwards and represents an apical horn; its basal part is enclosed as "columella" in the cavity of the simple shell, the lattice-work of which connects the four spines (compare above, Plectaniscus, p. 924). In the genus Euscenium, the simplest of all, the columella is simple, and the three feet also simple, without wings.

Subgenus 1. Euscenarium, Haeckel.

Shell three-sided pyramidal, thorny, about as long as broad, with three dentate edges. Framework very loose, with irregular polygonal meshes; in the middle of each of the three triangular sides a horizontal band of denser network. Basal plate with three very large simple collar-holes. The apical horn and the three feet are three-sided pyramidal, about half as long as the columella, with three prominent irregularly dentate edges. The horn is straight, whilst the three feet are hook-shaped, its distal end being curved downwards and inwards.

Shell three-sided pyramidal, smooth, nearly as long as broad, with three straight edges connected by irregular loose framework with polygonal meshes. Basal plate with three very large {1147}simple collar-holes. The apical horn and the three feet are three-sided prismatic, smooth, about twice as long as the columella, straight and widely divergent.

Shell hemispherical smooth, half as long as broad, with small and numerous subregular circular pores. Basal plate with three large triangular simple collar-holes. Horn slender, three-sided prismatic, twice as long as the columella. Feet very slender, with three denticulate edges, widely divergent and curved like the quadrant of a circle.

Archiscenium tricolpium, Haeckel, 1881, Prodromus et Atlas, loc. cit.

Shell cap-shaped, nearly hemispherical, with three vaulted hemispherical bosoms between the three arches ascending from the feet to the horn. Network very irregular, with polygonal meshes, of different form and size. Basal plate with three large primary and some smaller irregular accessory collar-holes. Horn slender, straight, twice as long as the columella. Feet of the same length, slender, widely divergent, slightly curved. The three edges of the horn and the feet are elegantly denticulated.

Tripospyris euscenium, Haeckel, 1881, Prodromus et Atlas.

Shell nearly spherical, smooth, with numerous small circular pores. Basal plate also with numerous small pores. Horn and feet stout, three-sided prismatic, straight or slightly curved, about as long as the thin, somewhat curved columella. This species is closely allied to Tripospyris.

Subgenus 2. Euscenidium, Haeckel.

Shell campanulate, smooth, with numerous irregular roundish pores. Basal plate with nine pores (three larger central and six smaller distal). Horn club-shaped, half as long as the columella. {1148}Feet twice as long, cylindrical, parallel, vertical, forked at the distal end. (Similar to Tripospyris semantis, Pl. 84, fig. 2, but without sagittal feet.)

Shell campanulate, smooth with subregular square pores. Basal plate with three large pores. Horn and feet of the same size and shape, twice as long as the columella, three-sided prismatic, each with four or five verticils of lateral branches. (Similar to the cephalis of Clathrocorys murrayi, Pl. 64, fig. 8, but with four free spines without connecting lattice-wings.)

Shell subspherical, rough, with small subregular circular pores. Basal plate with nine pores (three larger central and six smaller distal pores). Horn and feet of the same size and form, three to four times as long as the columella, three-sided prismatic, irregularly branched.

Genus 505. Cladoscenium,^[122] Haeckel, 1881, Prodromus, p. 429.

Definition.—Archiperida (vel Monocyrtida triradiata clausa) with a free branched internal columella, prolonged into an apical horn. Three basal feet free, without lateral wings.

The genus Cladoscenium differs from the preceding Euscenium only in the ramification of the internal columella, which bears one or more verticils of three ascending lateral branches. The three branches of each verticil lie in the same equidistant meridian planes as the three basal feet, and are inserted with their distal ends on the inner surface of the simple lattice-shell. The three feet are also branched, but without vertical lattice-wings. Cladoscenium is perhaps closely allied to Clathrocorys.

Shell subspherical, smooth, with large irregular roundish pores. Basal plate with three large pores. Columella with a single verticil of three ascending lateral branches. Apical horn as long as the {1149}columella, simple, three-sided prismatic. Feet twice as long, widely divergent, straight, prismatic, with some irregular basal branches.

Shell campanulate, smooth, with irregular polygonal pores. Basal plate with six pores (two large cardinal, two smaller jugular and two still smaller cervical pores). Columella with a single verticil of three ascending lateral branches (by mistake not distinct in the figure). Apical horn and the three feet of the same form and size, slender, prismatic, twice to three times as long as the shell, straight, in the distal half with three slender recurved branches, anchor-shaped.

Shell subspherical, with irregular polygonal pores. Basal plate with three large pores. Columella with two verticils of three ascending lateral branches. Apical horn as long as the columella, three-sided prismatic. Feet of the same form, twice as long, in the distal half with two opposite transverse branches, sword-shaped.

Shell campanulate, with irregular polygonal pores. Basal plate with four pores (two major cardinal and two minor jugular). Columella with two verticils of three ascending lateral branches, and prolonged into a slender prismatic apical horn of twice the length, which bears four such verticils. Feet twice as long as the horn, pinnate, each with four or five pairs of opposite lateral branches, decreasing towards the thin distal end.

Shell campanulate, with subregular square pores. Basal plate with nine pores (three larger central and six smaller distal). Columella with three verticils of three ascending lateral branches. Apical horn and the three basal feet of equal size and similar form, four to six times as long as the columella, three-sided prismatic, each with four to five verticils of three lateral branches, which are {1150}irregularly ramified and tapering towards the distal end. (Similar to Clathrocorys teuscheri, Pl. 64, fig. 10, but with four free spines, without connecting lattice-wings.)

Shell subspherical, with irregular roundish pores. Basal plate with three large holes. Columella with two verticils of three ascending lateral branches. Apical horn and the three feet of nearly the same size and form, three to four times as long as the columella, straight, three-sided prismatic, each with five to eight verticils of three simple lateral branches, tapering towards the distal end.

Genus 506. Archiscenium,^[123] Haeckel, 1881, Prodromus, p. 429.

Definition.—Archiperida (vel Monocyrtida triradiata clausa) with a free simple internal columella, prolonged into an apical horn. Three basal feet connected with the horn by three vertical lateral wings.

The genus Archiscenium and the following nearly allied Pteroscenium are derived from the two preceding genera, from which they differ in the development of three free vertical lateral lattice-wings; these arise from the upper edge of the three basal feet and connect them with the three edges of the apical horn. The basal part of the latter, enclosed in the shell, forms an internal free columella, which in Archiscenium is simple, not branched.

Shell hemispherical, smooth, with a small number of large irregular polygonal meshes and thin bars. Basal lattice with three very large central meshes and six smaller peripheral meshes (two on the base of each foot). Apical horn and the three feet of equal size and similar form, slender, pyramidal, widely divergent, straight, as long as the shell-diameter. Three lateral wings small, little prominent, each with two or three irregular meshes. Central capsule subspherical.

Shell campanulate, smooth, with numerous irregular square meshes. Basal lattice with three very large meshes. Apical horn and the three feet of equal size and similar form, three-sided prismatic, {1151}widely divergent, straight, twice as long as the shell-diameter. Three lateral wings broad, each with a basal row of few very large irregular roundish meshes, and several distal rows of small square meshes. This species is very similar to Clathrocorys murrayi (Pl. 64, fig. 8), but has no trace of thorax-wall. The latter species may be derived from the former by development of the thoracic lattice, which connects the three free feet.

Shell hemispherical, smooth, with numerous irregular roundish meshes of very different sizes. Basal lattice with four large meshes, two major cardinal and two minor cardinal pores. Apical horn and the three feet of similar form and size, slender prismatic, three to four times as long as the shell; the horn straight, the feet curved. Three lateral wings very delicate, with a basal row of few large irregular polygonal meshes, and several distal rows of similar small pores.

Shell hemispherical, with small irregular roundish pores. Basal lattice with four large meshes, two major cardinal and two minor jugular pores. Apical horn and the three feet of similar form and size, slender prismatic, straight, twice to four times as long as the shell. Three lateral wings nearly semicircular, densely latticed, with the same pores as the shell, and smooth convex margin.

Shell campanulate, with irregular polygonal pores. Basal lattice with nine meshes (three larger central and six smaller distal pores, as in Callimitra carolotæ, Pl. 63, fig. 8). Apical horn straight, prismatic, slender, conical, twice as long as the shell. Feet longer and more slender, slightly curved. Three lateral wings very broad, densely fenestrated, with irregular polygonal pores of the same shape as in the similar Callimitra carolotæ (Pl. 63, fig. 1).

Genus 507. Pteroscenium,^[124] Haeckel, 1881, Prodromus, p. 429.

Definition.—Archiperida (vel Monocyrtida triradiata clausa) with a free branched internal columella, prolonged into an apical horn. Three basal feet connected with the horn by three vertical lateral wings.

The genus Pteroscenium differs from the preceding Archiscenium only in the ramification of the internal columella, and therefore exhibits to it the same relation that Cladoscenium bears to Euscenium. The branches of the columella form also here verticils of ascending branches, three in each verticil, and their distal ends are inserted on the inner surface of the lattice-shell.

Shell campanulate, smooth, nearly conical, somewhat broader than long, with irregular dense network of small circular pores. Columella straight, with two or three triradiate verticils of horizontal lateral branches, which are inserted in the shell-wall. Horn slender pyramidal, as long as the shell. Three divergent feet twice as long as the horn, strongly curved, thorny, three-edged; the distance of their pointed ends twice as broad as the shell. From the outer edge of each foot arise numerous ascending bristles, which are connected together and with similar lateral branches of the horn by curved arches, forming three delicate spiny vertical wings.

Shell campanulate, smooth, with irregular polygonal pores, very similar to the preceding species but with much broader wings, forming several arcades with three to five rows of irregular meshes. Columella with five or six triradiate verticils of lateral branches. Horn twice as long as the shell, of the same length as the strongly curved spinulate feet.

SECOND PART.						PAGE
II.	Subclass OSCULOSA,					889
		Legion III. NASSELLARIA vel MONOPYLEA,				889
			Order	11.	Nassoidea,	895
			"	12.	Plectoidea,	898
			"	13.	Stephoidea,	931
			"	14.	Spyroidea,	1015
			"	15.	Botryodea,	1103
			"	16.	Cyrtoidea,	1126
		Legion IV. PHÆODARIA vel CANNOPYLEA,				1521
			Order	17.	Phæocystina,	1542
			"	18.	Phæosphæria,	1590
			"	19.	Phæogromia,	1642
			"	20.	Phæoconchia,	1710
Note on the Dimensions and Measurements,						1760
ADDENDA,						1761
ERRATA,						1763
INDEX,						1765

I. Order PLECTELLARIA. Nassellaria without complete lattice-shell.	No skeleton,	1. Nassoidea.
	Skeleton with a basal tripod, without ring,	2. Plectoidea.
	Skeleton with a sagittal ring (usually without tripod),	3. Stephoidea.
II. Order CYRTELLARIA. Nassellaria with a complete lattice-shell.	Cephalis bilocular, with a sagittal constriction,	4. Spyroidea.
	Cephalis multilocular, with two or more constrictions and lobes,	5. Botryodea.
	Cephalis simple, without constriction and lobes,	6. Cyrtoidea.

I. Order PLECTELLARIA. Nassellaria without complete lattice-shell.
	No skeleton,
	No skeleton,
		1. Nassoidea.
		1. Nassoidea.
	Skeleton with a basal tripod, without ring,
	Skeleton with a basal tripod, without ring,
		2. Plectoidea.
		2. Plectoidea.
	Skeleton with a sagittal ring (usually without tripod),
	Skeleton with a sagittal ring (usually without tripod),
		3. Stephoidea.
		3. Stephoidea.
II. Order CYRTELLARIA. Nassellaria with a complete lattice-shell.
	Cephalis bilocular, with a sagittal constriction,
	Cephalis bilocular, with a sagittal constriction,
		4. Spyroidea.
		4. Spyroidea.
	Cephalis multilocular, with two or more constrictions and lobes,

		5. Botryodea.
		5. Botryodea.
	Cephalis simple, without constriction and lobes,
	Cephalis simple, without constriction and lobes,
		6. Cyrtoidea.
		6. Cyrtoidea.

Calymma hyaline, without alveoles,	382. Cystidium.
Calymma foamy, with numerous large alveoles,	383. Nassella.

I. Skeleton (originally tripodal) composed of radial spines united in a common centre and supporting the central capsule, without wicker-work,	1. Plagonida.
II. Skeleton (originally tripodal) wattled, with irregular wicker-work, composed of the united branches of radial spines and enveloping the central capsule,	2. Plectanida.

I. Subfamily Triplagida. Three radial spines.	Three spines lying in one horizontal plane,		384. Triplagia.
	Three spines corresponding to the edges of a flat pyramid,		385. Plagiacantha.
II. Subfamily Tetraplagida. Four radial spines.	Four spines arising from one common central point.	All four spines equal,	386. Tetraplagia.
		One apical spine opposed to three basal spines,	387. Plagoniscus.
	Four spines arising in two pairs from the poles of a common central rod.	All four spines equal,	388. Plagonidium.
		One apical spine opposed to three basal spines,	389. Plagiocarpa.
III. Subfamily Hexaplagida. Six radial spines.	Six spines arising from one common central point,		390. Hexaplagia.
	Six spines arising in two opposite groups from the poles of a common central rod,		391. Plagonium.
IV. Subfamily Polyplagida. Numerous radial spines.	Numerous (seven to nine or more) radial spines arising from a common centre (either a central point or a branched rod),		392. Polyplagia.

I. Subfamily Triplagida. Three radial spines.
	Three spines lying in one horizontal plane,
	Three spines lying in one horizontal plane,
			384. Triplagia.
			384. Triplagia.
	Three spines corresponding to the edges of a flat pyramid,
	Three spines corresponding to the edges of a flat pyramid,
			385. Plagiacantha.
			385. Plagiacantha.
II. Subfamily Tetraplagida. Four radial spines.
	Four spines arising from one common central point.
	Four spines arising from one common central point.
		All four spines equal,
		All four spines equal,
			386. Tetraplagia.
			386. Tetraplagia.
		One apical spine opposed to three basal spines,
		One apical spine opposed to three basal spines,
			387. Plagoniscus.
			387. Plagoniscus.
	Four spines arising in two pairs from the poles of a common central rod.

		All four spines equal,
		All four spines equal,
			388. Plagonidium.
			388. Plagonidium.
		One apical spine opposed to three basal spines,
		One apical spine opposed to three basal spines,
			389. Plagiocarpa.
			389. Plagiocarpa.
III. Subfamily Hexaplagida. Six radial spines.
	Six spines arising from one common central point,
	Six spines arising from one common central point,
			390. Hexaplagia.
			390. Hexaplagia.
	Six spines arising in two opposite groups from the poles of a common central rod,

			391. Plagonium.
			391. Plagonium.
IV. Subfamily Polyplagida. Numerous radial spines.
	Numerous (seven to nine or more) radial spines arising from a common centre (either a central point or a branched rod),

			392. Polyplagia.
			392. Polyplagia.

I. Subfamily Triplectida. Three radial spines.	Three spines lying in one horizontal plane,		393. Triplecta.
	Three spines corresponding to the edges of a flat pyramid,		394. Plectophora.
II. Subfamily Tetraplectida Four radial spines.	Four spines arising from one common central point.	All four spines equal,	395. Tetraplecta.
		One apical spine opposed to three basal spines,	396. Plectaniscus.
	Four spines arising in two pairs from the poles of a common central rod; one apical spine different from three basal spines,		397. Periplecta.
III. Subfamily Hexaplectida. Six radial spines.	Six spines arising from one common central point,		398. Hexaplecta.
	Six spines arising in two opposite groups from the poles of a common control rod,		399. Plectanium.
IV. Subfamily Polyplectida. Numerous radial spines.	Numerous (seven to nine or more) radial spines arising from a common centre (either a central point or a branched rod),		400. Polyplecta.

I. Skeleton composed of the simple vertical sagittal ring only, without secondary rings,	1. Stephanida.
II. Skeleton composed of two crossed rings, a vertical sagittal and a horizontal basal ring,	2. Semantida.
III. Skeleton composed of two crossed vertical meridional rings (a primary sagittal and a secondary frontal ring), commonly also with a horizontal basal ring,	3. Coronida.
IV. Skeleton composed of two parallel horizontal rings (upper mitral and lower basal ring), both connected by a vertical sagittal ring (and often by a vertical frontal ring),	4. Tympanida.

I. Subfamily Lithocircida. No typical basal feet on the base of the ring (no cortinar feet).	Ring diphragmatic or amphithect; dorsal and ventral bow equal.	Ring smooth or thorny, without branched spines.	401. Archicircus.
		Ring armed with branched spines,	402. Lithocircus.
	Ring dipleuric, bilateral; dorsal and ventral bow different.	Ring smooth or thorny, without branched spines,	403. Zygocircus.
		Ring armed with branched spines.	404. Dendrocircus.
II. Subfamily Cortinida. Three or four typical basal feet on the ring (cortinar feet).	Three basal feet (and an apical horn).	One caudal and two lateral feet,	405. Cortina.
	Four basal feet (and an apical horn).	Two sagittal and two lateral feet,	406. Stephanium.

I. Subfamily Lithocircida. No typical basal feet on the base of the ring (no cortinar feet).
	Ring diphragmatic or amphithect; dorsal and ventral bow equal.

		Ring smooth or thorny, without branched spines.
		Ring smooth or thorny, without branched spines.
			401. Archicircus.
			401. Archicircus.
		Ring armed with branched spines,
		Ring armed with branched spines,
			402. Lithocircus.
			402. Lithocircus.
	Ring dipleuric, bilateral; dorsal and ventral bow different.

		Ring smooth or thorny, without branched spines,
		Ring smooth or thorny, without branched spines,
			403. Zygocircus.
			403. Zygocircus.
		Ring armed with branched spines.
		Ring armed with branched spines.
			404. Dendrocircus.
			404. Dendrocircus.
II. Subfamily Cortinida. Three or four typical basal feet on the ring (cortinar feet).
	Three basal feet (and an apical horn).
	Three basal feet (and an apical horn).
		One caudal and two lateral feet,
		One caudal and two lateral feet,
			405. Cortina.
			405. Cortina.
	Four basal feet (and an apical horn).
	Four basal feet (and an apical horn).
		Two sagittal and two lateral feet,
		Two sagittal and two lateral feet,
			406. Stephanium.
			406. Stephanium.

I. Subfamily Semantiscida. Basal ring without typical, regularly disposed basal feet (no cortinar feet).	Only two, four, or six basal pores (no dorsal and ventral pores).	Two basal pores,	407. Semantis.
		Four basal pores,	408. Semantrum.
		Six basal pores,	409. Semantidium.
	Besides four basal pores, also apical pores or dorsal and ventral pores along the whole ring,		410. Clathrocircus.
II. Subfamily Cortiniscida. Basal ring with typical, regularly disposed basal feet (cortinar feet).	Three basal feet.	One odd caudal foot and two paired lateral feet,	411. Cortiniscus.
	Four basal feet.	Two sagittal and two lateral or pectoral feet,	412. Stephaniscus.
	Six basal feet.	Two sagittal, two pectoral, and two tergal feet,	413. Semantiscus.

I. Subfamily Semantiscida. Basal ring without typical, regularly disposed basal feet (no cortinar feet).
	Only two, four, or six basal pores (no dorsal and ventral pores).

		Two basal pores,
		Two basal pores,
			407. Semantis.
			407. Semantis.
		Four basal pores,
		Four basal pores,
			408. Semantrum.
			408. Semantrum.
		Six basal pores,
		Six basal pores,
			409. Semantidium.
			409. Semantidium.
	Besides four basal pores, also apical pores or dorsal and ventral pores along the whole ring,

			410. Clathrocircus.
			410. Clathrocircus.
II. Subfamily Cortiniscida. Basal ring with typical, regularly disposed basal feet (cortinar feet).
	Three basal feet.
	Three basal feet.
		One odd caudal foot and two paired lateral feet,
		One odd caudal foot and two paired lateral feet,
			411. Cortiniscus.
			411. Cortiniscus.
	Four basal feet.
	Four basal feet.
		Two sagittal and two lateral or pectoral feet,
		Two sagittal and two lateral or pectoral feet,
			412. Stephaniscus.
			412. Stephaniscus.
	Six basal feet.
	Six basal feet.
		Two sagittal, two pectoral, and two tergal feet,
		Two sagittal, two pectoral, and two tergal feet,
			413. Semantiscus.
			413. Semantiscus.

I. Subfamily Zygostephanida. Four lateral gates (no basal gate).	Two meridional rings (sagittal and frontal) complete, perpendicular to one another (no basal ring).	Four lateral gates simple,		414. Zygostephanus.
		Four lateral gates partly latticed,		415. Zygostephanium.
II. Subfamily Acanthodesmida. Five large gates (four lateral and one simple basal).	Two meridional rings (sagittal and frontal) incomplete, both truncated by the complete horizontal basal ring.	Four lateral gates simple,		416. Coronidium.
		Four lateral gates partly latticed,		417. Acanthodesmia.
III. Subfamily Eucoronida. Six large gates (four lateral and two basal).	Two rings (the sagittal meridional ring and the horizontal basal ring) complete, the frontal meridian ring incomplete.	Basal ring without larger descending feet.	Gates simple,	418. Eucoronis.
			Gates partly latticed,	419. Plectocoronis.
		Basal ring with large, regularly disposed, descending feet. Gates simple,		420. Podocoronis.
IV. Subfamily Trissocyclida. Eight large gates (four upper lateral and four lower basal).	Two meridional rings (sagittal and frontal) and the horizontal basal ring complete. All three complete rings perpendicular to one another.	Four upper gates larger than the four lower.	Gates simple,	421. Tristephanium.
			Gates partly latticed,	422. Tricyclidium.
		All eight gates of equal size.	Gates simple,	423. Trissocircus.
			Gates partly latticed,	424. Trissocyclus.

I. Subfamily Zygostephanida. Four lateral gates (no basal gate).
	Two meridional rings (sagittal and frontal) complete, perpendicular to one another (no basal ring).

		Four lateral gates simple,
		Four lateral gates simple,
				414. Zygostephanus.
				414. Zygostephanus.
		Four lateral gates partly latticed,
		Four lateral gates partly latticed,
				415. Zygostephanium.
				415. Zygostephanium.
II. Subfamily Acanthodesmida. Five large gates (four lateral and one simple basal).
	Two meridional rings (sagittal and frontal) incomplete, both truncated by the complete horizontal basal ring.

		Four lateral gates simple,
		Four lateral gates simple,
				416. Coronidium.
				416. Coronidium.
		Four lateral gates partly latticed,
		Four lateral gates partly latticed,
				417. Acanthodesmia.
				417. Acanthodesmia.
III. Subfamily Eucoronida. Six large gates (four lateral and two basal).
	Two rings (the sagittal meridional ring and the horizontal basal ring) complete, the frontal meridian ring incomplete.

		Basal ring without larger descending feet.
		Basal ring without larger descending feet.
			Gates simple,
			Gates simple,
				418. Eucoronis.
				418. Eucoronis.
			Gates partly latticed,
			Gates partly latticed,
				419. Plectocoronis.
				419. Plectocoronis.
		Basal ring with large, regularly disposed, descending feet. Gates simple,

				420. Podocoronis.
				420. Podocoronis.
IV. Subfamily Trissocyclida. Eight large gates (four upper lateral and four lower basal).
	Two meridional rings (sagittal and frontal) and the horizontal basal ring complete. All three complete rings perpendicular to one another.

		Four upper gates larger than the four lower.
		Four upper gates larger than the four lower.
			Gates simple,
			Gates simple,
				421. Tristephanium.
				421. Tristephanium.
			Gates partly latticed,
			Gates partly latticed,
				422. Tricyclidium.
				422. Tricyclidium.
		All eight gates of equal size.
		All eight gates of equal size.
			Gates simple,
			Gates simple,
				423. Trissocircus.
				423. Trissocircus.
			Gates partly latticed,
			Gates partly latticed,
				424. Trissocyclus.
				424. Trissocyclus.

I. Subfamily Protympanida. Two horizontal rings (upper mitral ring and lower basal ring) bisected by the complete sagittal ring.	Two horizontal rings connected by two columellæ.		One complete sagittal ring (no frontal ring),	425. Protympanium.
	Two horizontal rings connected by four columellæ (the halves of the sagittal and the frontal ring).	No equatorial ring.	No galear and thoracal bows,	426. Acrocubus.
			Galear and thoracal bows,	427. Toxarium.
		An equatorial ring.	Equatorial ring complete,	428. Microcubus.
			Equatorial ring incomplete,	429. Octotympanum.
	Two horizontal rings connected by six or eight columellæ (three or four vertical rings).		Six columellæ (three meridional rings),	430. Tympaniscus.
			Eight columellæ (four meridional rings),	431. Tympanidium.
II. Subfamily Paratympanida. Two horizontal rings fenestrated.	Two horizontal rings closed by a lattice-plate, connected by numerous columellæ.		Two rings unequal (columellæ divergent),	432. Paratympanum.
			Two rings equal (columellæ parallel),	433. Lithotympanum.

III. Subfamily Dystympanida. Mitral ring fenestrated, basal ring simple.	Two horizontal rings connected by numerous (six to eight or more columellæ).	Mitral ring closed by a lattice-plate, basal ring simple,		434. Dystympanium.
IV. Subfamily Eutympanida. Two horizontal rings (upper mitral ring and lower basal ring) simple. Apical and basal parts of the sagittal ring lost.	Two horizontal rings connected by two or three columellæ (four or five open gates).	Two columellæ (parts of the sagittal ring),		435. Parastephanus.
		Three columellæ (parts of the half sagittal and the frontal ring),		436. Prismatium.
	Two horizontal rings connected by four or more columellæ (six or eight or more open gates).	Four columellæ	Two rings unequal,	437. Pseudocubus.
			Two rings equal,	438. Lithocubus.
		Six to eight or more columellæ.	Two rings unequal,	439. Circotympanum.
			Two rings equal,	440. Eutympanium.

Shell without thorax; no second shell-joint, developed from the base of the cephalis.	Cephalis without galea (or apical cupola),	1. Zygospyrida.
	Cephalis with a galea (or apical cupola),	2. Tholospyrida.
Shell with a thorax, or a second shell-joint, developed from the base of the cephalis.	Cephalis without galea (or apical cupola),	3. Phormospyrida.
	Cephalis with a galea (or apical cupola),	4. Androspyrida.

I. Subfamily Tripospyrida. Three basal feet. (One odd caudal and two paired pectoral.)	Apex of the shell with one horn,			441. Tripospyris.
	Apex of the shell with three horns,			442. Triceraspyris.
	Apex of the shell without horns,			443. Tristylospyris.
	Apex with two large coryphal holes, right and left,			444. Cephalospyris.
II. Subfamily Dipospyrida. Two basal lateral feet. (Originally the two pectoral feet.)	Two feet free, not grown together.	Feet simple, not branched, without lateral spines.	One horn,	445. Dipospyris.
			No horn,	446. Brachiospyris.
		Feet branched like a tree.	One horn,	447. Dendrospyris.
		Feet with a series of lateral spines.	One horn,	448. Dorcadospyris.
	Two feet grown together and uniting to form a ring. Apex with a horn.	Feet simple,		449. Gamospyris.
		Feet with a series of lateral spines,		450. Stephanospyris.
III. Subfamily Tetraspyrida. Two sagittal and two lateral feet.	Feet simple, not branched.	Apex with one horn,		451. Tetraspyris.
		Apex without a horn,		452. Tessarospyris.
IV. Subfamily Hexaspyrida. Six basal feet.	Two sagittal, two pectoral, and two tergal feet.	Apex with one horn,		453. Hexaspyris.
		Apex with three horns,		454. Liriospyris.
		Apex without a horn,		455. Cantharospyris.
V. Subfamily Pentaspyrida. Five basal feet.	One caudal, two pectoral, and two tergal feet.	Apex with one horn,		456. Clathrospyris.
		Apex with three horns,		457. Ægospyris.
		Apex without a horn,		458. Pentaspyris.
VI. Subfamily Therospyrida. Four paired lateral feet. (Two pectoral and two tergal.)	Apex with one horn,			459. Zygospyris.
	Apex with three horns (one apical and two frontal),			460. Elaphospyris.
	Apex with two lateral or frontal horns,			461. Taurospyris.
	Apex without a horn,			462. Therospyris.
VII. Subfamily Polyspyrida. Numerous (seven to twelve or more) basal feet.	Apex with one horn,			463. Petalospyris.
	Apex with three horns (one apical and two frontal),			464. Anthospyris.
	Apex with numerous horns,			465. Ceratospyris.
	Apex without a horn,			466. Gorgospyris.
VIII. Subfamily Circospyrida. No basal feet.	Apex with one horn,			467. Circospyris.
	Apex without a horn,			468. Dictyospyris.

I. Subfamily Lophospyrida. Two or three basal (cortinar feet). Galea with a horn.	Three basal feet (two paired pectoral and an odd caudal),	469. Tholospyris.
	Two paired basal (pectoral) feet,	470. Lophospyris.
II. Subfamily Tiarospyrida. Numerous basal feet in a corona (six to nine or more).	Galea with a horn,	471. Sepalospyris.
	Galea without a horn,	472. Tiarospyris.
III. Subfamily Pylospyrida. No basal feet.	Galea with a horn,	473. Pylospyris.

I. Subfamily Acrospyrida. Three basal cortinar feet (one odd caudal and two paired pectoral).	One apical horn,	474. Acrospyris.
	No apical horn,	475. Phormospyris.
II. Subfamily Rhodospyrida. Numerous basal feet in a corona (nine to twelve or more.)	One apical horn,	476. Patagospyris.
	Three apical horns,	477. Rhodospyris.
	No apical horn,	478. Desmospyris.

I. Subfamily Lamprospyrida. Three free basal feet.	Lattice-work simple, not spongy.	Apical horn usually simple, not fenestrated,	479. Androspyris.
	Lattice-work wholly or partly spongy.	Apical horn usually branched and fenestrated,	480. Lamprospyris.
II. Subfamily Perispyrida. No free basal feet. Shell three-jointed.	Shell with two transverse coronal strictures (one superior mitral and one inferior collar stricture).	Lattice-work only complete in the frontal ring,	481. Amphispyris.
		Lattice-work complete on all sides,	482. Tricolospyris.
		Lattice-work double or spongy,	483. Perispyris.
III. Subfamily Nephrospyrida. No free basal feet. Shell spherical or discoidal.	Shell without external transverse stricture.	Shell spherical or subspherical,	484. Sphærospyris.
		Shell discoidal, kidney-shaped or subcircular,	485. Nephrospyris.

1. Shell monothalamous, consisting of the lobate cephalis only,	1. Cannobotryida.
2. Shell dithalamous, composed of a lobate cephalis and a simple thorax,	2. Lithobotryida.
3. Shell trithalamous, composed of a lobate cephalis, a thorax and an abdomen,	3. Pylobotryida.

Cephalis without porous tubes,	486. Botryopera.
Cephalis with a variable number of porous tubes,	487. Cannobotrys.

I. Subfamily Botryopylida. Mouth of the thorax open.	Cephalis without porous tubes,	488. Botryopyle.
	Cephalis with a variable number of porous tubes,	489. Acrobotrys.
II. Subfamily Botryocellida. Mouth of the thorax closed by a lattice-plate.	Cephalis without porous tubes,	490. Botryocella.
	Cephalis with a variable number of porous tubes,	491. Lithobotrys.

The Project Gutenberg eBook, Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, Second Part: Subclass Osculosa; Index, by Ernst Haeckel

Legion III. NASSELLARIA,

Synopsis of the Orders and Suborders of Nassellaria.

Order V. PLECTELLARIA, Haeckel, 1883.

Suborder I. NASSOIDEA, Haeckel.

Family XLV. Nassellida, Haeckel.

Synopsis of the Genera of Nassellida.

Genus 382. Cystidium,[1] R. Hertwig, 1879, Organismus d. Radiol., p. 87.

Genus 383. Nassella,[2] nov. gen.

Suborder II. PLECTOIDEA, Haeckel.

Synopsis of the Families of Plectoidea.

Family XLVI. Plagonida, Haeckel.

Synopsis of the Genera of Plagonida.

Subfamily 1. Triplagida, Haeckel, 1881, Prodromus, p. 423.

Genus 384. Triplagia,[3] Haeckel, 1881, Prodromus, p. 423.

Genus 385. Plagiacantha,[4] Claparède, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, November 13.

Subfamily 2. Tetraplagida, Haeckel, 1881, Prodromus, p. 424.

Genus 386. Tetraplagia,[5] Haeckel, 1881, Prodromus, p. 424.

Genus 387. Plagoniscus,[6] n. gen.

Genus 388. Plagonidium,[7] Haeckel, 1881, Prodromus, p. 424.

Genus 389. Plagiocarpa,[8] Haeckel, 1881, Prodromus, p. 424.

Subfamily 3. Hexaplagida, Haeckel.

Genus 390. Hexaplagia,[9] Haeckel, 1881, Prodromus, p. 424.

Genus 391. Plagonium,[10] Haeckel, 1881, Prodromus, p. 423.

Subfamily 4. Polyplagida, Haeckel, 1881, Prodromus, p. 424.

Genus 392. Polyplagia,[11] n. gen.

Family XLVII. Plectanida, Haeckel.

Synopsis of the Genera of Plectanida.

Subfamily 1. Triplectida, Haeckel, 1881, Prodromus, p. 424.

Genus 393. Triplecta,[12] Haeckel, 1881, Prodromus, p. 424.

Genus 394. Plectophora,[13] Haeckel, 1881, Prodromus, p. 424.

Subfamily 2. Tetraplectida, Haeckel, 1881, Prodromus, p. 424.

Genus 395. Tetraplecta,[14] Haeckel, 1881, Prodromus, p. 424.

Genus 396. Plectaniscus,[15] nov. gen.

Genus 397. Periplecta,[16] Haeckel, 1881, Prodromus, p. 424.

Subfamily 3. Hexaplectica, Haeckel.

Genus 398. Hexaplecta,[17] Haeckel, 1881, Prodromus, p. 425.

Genus 399. Plectanium,[18] Haeckel, 1881, Prodromus, p. 424.

Subfamily 4. Polyplectida, Haeckel, 1881, Prodromus, p. 424.

Genus 400. Polyplecta,[19] Haeckel.

Suborder III. STEPHOIDEA, Haeckel.

Synopsis of the Families of Stephoidea.

Family XLVIII. Stephanida, Haeckel (Pl. 81).

Synopsis of the Genera of Stephanida.

Subfamily 1. Lithocircida, Haeckel.

Genus 401. Archicircus,[20] n. gen.

Subgenus 1. Monostephus, Haeckel, 1881, Prodromus, p. 447.

Subgenus 2. Archistephus, Haeckel.

Genus 402. Lithocircus,[21] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Genus 403. Zygocircus,[22] Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 496.

Genus 404. Dendrocircus,[23] Haeckel, 1881, Prodromus, p. 447.

Subfamily 2. Cortinida, Haeckel.

Genus 405. Cortina,[24] n. gen.

Genus 406. Stephanium,[25] n. gen.

Family XLIX. Semantida, n. fam.

Synopsis of the Genera of Semantida.

Subfamily 1. Semantiscida, Haeckel.

Genus 407. Semantis,[26] n. gen.

Genus 408. Semantrum,[27] n. gen.

Genus 409. Semantidium,[28] n. gen.

Genus 410. Clathrocircus,[29] Haeckel, 1881, Prodromus, p. 447.

Subfamily 2. Cortiniscida, Haeckel.

Genus 411. Cortiniscus,[30] n. gen.

Genus 412. Stephaniscus,[31] n. gen.

Genus 413. Semantiscus,[32] n. gen.

Family L. Coronida, Haeckel.

Synopsis of the Genera of Coronida.

Subfamily 1. Zygostephanida, Haeckel, 1881, Prodromus, p. 446.

Genus 414. Zygostephanus,[33] Haeckel, 1862, Monogr. d. Radiol., p. 268.

Subgenus 1. Zygostephus, Haeckel, 1881, Prodromus, p. 446.

Subgenus 2. Zygostephaniscus, Haeckel, 1881, Prodromus, p. 446.

Genus 415. Zygostephanium,[34] Haeckel, 1881, Prodromus, p. 446.

Subfamily 2. Acanthodesmida, Haeckel, 1881, Prodromus, p. 445.

Genus 416. Coronidium,[35] Haeckel, 1881, Prodromus, p. 445.

Genus 417. Acanthodesmia,[36] J. Müller, 1856, Monatsber. d. k. preuss.

Subfamily 3. Eucoronida, Haeckel, 1881, Prodromus, p. 445.

Genus 418. Eucoronis,[37] Haeckel, 1881, Prodromus, p. 445.

Subgenus 1. Acrocoronis, Haeckel, 1881, Prodromus, p. 445.

Subgenus 2. Lithocoronis, Haeckel, 1881, Prodromus, p. 445.

Genus 419. Plectocoronis,[38] Haeckel, 1881, Prodromus, p. 445.

Genus 382. Cystidium,^[1] R. Hertwig, 1879, Organismus d. Radiol., p. 87.

Genus 383. Nassella,^[2] nov. gen.

Genus 384. Triplagia,^[3] Haeckel, 1881, Prodromus, p. 423.

Genus 385. Plagiacantha,^[4] Claparède, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, November 13.

Genus 386. Tetraplagia,^[5] Haeckel, 1881, Prodromus, p. 424.

Genus 387. Plagoniscus,^[6] n. gen.

Genus 388. Plagonidium,^[7] Haeckel, 1881, Prodromus, p. 424.

Genus 389. Plagiocarpa,^[8] Haeckel, 1881, Prodromus, p. 424.

Genus 390. Hexaplagia,^[9] Haeckel, 1881, Prodromus, p. 424.

Genus 391. Plagonium,^[10] Haeckel, 1881, Prodromus, p. 423.

Genus 392. Polyplagia,^[11] n. gen.

Genus 393. Triplecta,^[12] Haeckel, 1881, Prodromus, p. 424.

Genus 394. Plectophora,^[13] Haeckel, 1881, Prodromus, p. 424.

Genus 395. Tetraplecta,^[14] Haeckel, 1881, Prodromus, p. 424.

Genus 396. Plectaniscus,^[15] nov. gen.

Genus 397. Periplecta,^[16] Haeckel, 1881, Prodromus, p. 424.

Genus 398. Hexaplecta,^[17] Haeckel, 1881, Prodromus, p. 425.

Genus 399. Plectanium,^[18] Haeckel, 1881, Prodromus, p. 424.

Genus 400. Polyplecta,^[19] Haeckel.

Genus 401. Archicircus,^[20] n. gen.

Genus 402. Lithocircus,^[21] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Genus 403. Zygocircus,^[22] Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 496.

Genus 404. Dendrocircus,^[23] Haeckel, 1881, Prodromus, p. 447.

Genus 405. Cortina,^[24] n. gen.

Genus 406. Stephanium,^[25] n. gen.

Genus 407. Semantis,^[26] n. gen.

Genus 408. Semantrum,^[27] n. gen.

Genus 409. Semantidium,^[28] n. gen.

Genus 410. Clathrocircus,^[29] Haeckel, 1881, Prodromus, p. 447.

Genus 411. Cortiniscus,^[30] n. gen.

Genus 412. Stephaniscus,^[31] n. gen.

Genus 413. Semantiscus,^[32] n. gen.

Genus 414. Zygostephanus,^[33] Haeckel, 1862, Monogr. d. Radiol., p. 268.

Genus 415. Zygostephanium,^[34] Haeckel, 1881, Prodromus, p. 446.

Genus 416. Coronidium,^[35] Haeckel, 1881, Prodromus, p. 445.

Genus 417. Acanthodesmia,^[36] J. Müller, 1856, Monatsber. d. k. preuss.

Genus 418. Eucoronis,^[37] Haeckel, 1881, Prodromus, p. 445.

Genus 419. Plectocoronis,^[38] Haeckel, 1881, Prodromus, p. 445.

Genus 420. Podocoronis,^[39] Haeckel, 1881, Prodromus, p. 445.

Genus 421. Tristephanium,^[40] Haeckel, 1881, Prodromus, p. 445.

Genus 422. Tricyclidium,^[41] Haeckel, 1881, Prodromus, p. 446.

Genus 423. Trissocircus,^[42] Haeckel, 1881, Prodromus, p. 446.

Genus 424. Trissocyclus,^[43] Haeckel, 1881, Prodromus, p. 446.

Genus 425. Protympanium,^[44] Haeckel, 1881, Prodromus, p. 447 (sensu emend.).

Genus 426. Acrocubus,^[45] Haeckel, 1881, Prodromus, p. 447.

Genus 427. Toxarium,^[46] n. gen.

Genus 428. Microcubus,^[47] Haeckel, 1881, Prodromus, p. 447.

Genus 429. Octotympanum,^[48] n. gen.

Genus 430. Tympaniscus,^[49] n. gen.

Genus 431. Tympanidium,^[50] Haeckel, 1881, Prodromus, p. 447.

Genus 432. Paratympanum,^[51] Haeckel, 1881, Prodromus, p. 447.

Genus 433. Lithotympanum,^[52] Haeckel, 1881, Prodromus, p. 447.

Genus 434. Dystympanium,^[53] n. gen.

Genus 436. Prismatium,^[54] Haeckel, 1862, Monogr. d. Radiol., p. 270.

Genus 437. Pseudocubus,^[55] n. gen.

Genus 438. Lithocubus,^[56] Haeckel, 1881, Prodromus, p. 447.

Genus 439. Circotympanum,^[57] n. gen.

Genus 440. Eutympanium,^[58] Haeckel, 1881, Prodromus, p. 447.

Genus 441. Tripospyris,^[59] Haeckel, 1881, Prodromus, p. 441.

Genus 442. Triceraspyris,^[60] Haeckel, 1881, Prodromus, p. 441.

Genus 443. Tristylospyris,^[61] Haeckel, 1881, Prodromus, p. 441.

Genus 444. Cephalospyris,^[62] Haeckel, 1881, Prodromus, p. 441 (sensu emend.).

Genus 445. Dipospyris,^[63] Haeckel, 1881, Prodromus, p. 441.

Genus 446. Brachiospyris,^[64] Haeckel, 1881, Prodromus, p. 441.

I. Subfamily Botryocyrtida. Mouth of the abdomen open.	Cephalis without porous tubes,	492. Botryocyrtis.
	Cephalis with a variable number of porous tubes,	493. Pylobotrys.
II. Subfamily Botryocampida. Mouth of the abdomen closed by a lattice-plate.	Cephalis without porous tubes,	494. Botryocampe.
	Cephalis with a variable number of porous tubes,	495. Phormobotrys.

Family LIX. Tripocalpida. Three radial apophyses.	Mouth open,	1. Archipilida.
	Mouth closed,	2. Archiperida.
Family LX. Phænocalpida. Numerous radial apophyses.	Mouth open,	3. Archiphormida.
	Mouth closed,	4. Archiphænida.
Family LXI. Cyrtocalpida. No radial apophyses.	Mouth open,	5. Archicorida.
	Mouth closed,	6. Archicapsida.

I. Subfamily Archipilida. Basal mouth of the shell a simple wide opening.	Shell with three lateral ribs or wings, with or without terminal feet.	Three terminal feet.	Apex with a horn,	496. Tripocalpis.
			No apical horn,	497. Tripodonium.
		Six to nine or more terminal feet.	No apical horn,	498. Tripterocalpis.
		No terminal feet.	Apex with a horn,	499. Trissopilium.
			No apical horn,	500. Archipilium.
	Shell without lateral ribs or wings but with three terminal feet.	Feet simple or branched, not latticed.	Apex with a horn,	501. Tripilidium.
			No apical horn,	502. Tripodiscium.
		Feet latticed.	Apex with a horn,	503. Tridictyopus.
II. Subfamily Archiperida. Basal mouth of the shell closed by a lattice-plate.	Shell in its axis with a free (simple or branched) internal columella, prolonged into an apical horn.	Shell with three free feet, without lateral lattice-wings.	Columella simple,	504. Euscenium.
			Columella branched,	505. Cladoscenium.
		Shell with three lateral lattice-wings, connecting the three feet with the horn.	Columella simple,	506. Archiscenium.
			Columella branched,	507. Pteroscenium.
	Shell with simple cavity, without free columella. Three free basal feet.		One apical horn,	508. Peridium.
			Two or more horns,	509. Archipera.
			No apical horn,	510. Archibursa.