Transcriber Note -- Text emphasis denoted by _Italics_.




                             OBSERVATIONS

                                ON THE

                       TERATASPIS GRANDIS, Hall,

                     THE LARGEST KNOWN TRILOBITE.



                           BY J. M. CLARKE.




             OBSERVATIONS ON THE TERATASPIS GRANDIS, Hall,

                     The Largest Known Trilobite.


                           By J. M. CLARKE.


          Communicated to the State Geologist December, 1890.

Trilobites of great size have been reported from various formations.
With rare exceptions, however, these relics are but fragments of the
test, leaving to the imagination the restoration of the original
proportions of the animal, and without an earnest mental effort one is
apt to leave the contemplation of the large fragment with no adequate
conception of the imposing lineaments of its owner. Indications of
these gigantic forms occur in all the grand faunas of the Palæozoic,
with the exception of the Carboniferous where diminution in numbers
was accompanied by diminution in size, or, in other words, by the
prevalence of genera in which great size was never attained.

Almost with the earliest known appearance of the Trilobites the genus
PARADOXIDES attained magnificent proportions. _Paradoxides Harlani_,
the well-known species of the Braintree agilities, must have grown to
a length of 18 inches. ANGELIN has figured an entire specimen of _P.
Tessini_ 12 inches in length, and BARRANDE a fragment of an individual
of _P. imperialis_ which must have had about the same size. Mr. G. F.
MATTHEW has described a nearly entire individual of an immense _P.
regina_ from the St. John beds, 15 inches long and 12 inches across the
base of the cephalon, and it is claimed, with undoubted accuracy, that
this is the largest undismembered specimen of a trilobite found in any
country.

In the second faunas great Asaphids were not uncommon. As early as
1839 Dr. JOHN LOCKE described in the report of the Geological Survey
of Ohio, a portion of an immense pygidium to which he gave the name
_Isotelus maximus_. In 1843 Dr. LOCKE figured an entire individual of
what he considered the same species, changing the name, however, to
_Isotelus megistus_. This specimen measured nine and three-quarters
inches in length. The figure was accompanied by outlines of two large
pygidia, the greater of which was that referred to in 1839, which, the
author says, coincided "with the end of an ellipse 22 inches long
and 12 inches broad." This is an evidently much compressed fragment,
measuring seven inches in its greatest transverse diameter, and
assuming this as the greatest diameter of the pygidium and restoring
the length from the proportions of the animal as there given, the
original length of its owner would have been about 13 inches. The plate
is incomplete on its anterior portion, and it is probable that the
error in this estimate due to the exaggeration of size from compression
of the shield, is compensated by the loss of diameter from imperfect
retention. This great pygidium, with other large fragments of the same
species, were used as a basis for a well-known restoration in plaster
to be found in some of the older museums of this country. ANGELIN has
given a restoration of _Megalaspis heros_ 14 inches in length and
BRÖGGER estimated the original length of _Megalaspis acuticauda_ to
be fully 16 inches. BARRANDE figured an entire _Asaphus nobilis_ from
Etage D which measures 10½ inches.

Not until the introduction of the genera DALMANITES, HOMALONOTUS
and LICHAS do we meet with the most gigantic proportions attained
by these crustaceans, and then only after these genera have become
well established. Perhaps none of their representatives in the lower
Silurian faunas were of commanding size; in the upper Silurian large
but not extravagant proportions were sometimes attained. _Lichas
Boltoni_ of the Niagara fauna, is a magnificent species, one of the
largest of its race and remarkable for the frequency with which its
parts are found together, an extremely uncommon occurrence in this
thin-shelled group. The _Lichas pustulosus_ of the Lower Helderberg
shaly limestone was a great species attaining a length of 10 inches
or more. _Homalonotus delphinocephalus_ of the Niagara fauna grew to
large size but does not appear to have attained the length of its
successor in the Lower Helderberg, _H. Vanuxemi_, which, according to
the restoration from a very large fragment given in the Palæontology
of New York, Volume VII (plate V B) grew to a length of at least 11½
inches. SALTER has mentioned (Palæontographical Society, vol. xvii, p.
109) a large fragment of _Homalonotus rudis_ which he estimates may
have been a foot in length. In later faunas are found traces of this
genus of still greater size. Dr. BRUSHAUSEN has figured a pygidium of
_H. gigas_ from the Spiriferen-sandstein of the Hartz, the possessor
of which must have been upward of one foot in length. Unquestionably
the largest individual of HOMALONOTUS known is that of _H. major_,
from the Oriskany sandstone, figured in the Palæontology of New York,
Volume VII (plate V A), a large fragment representing the greater part
of the thorax and the pygidium, and according to the restoration there
given the original length of the animal must have been well nigh 15
inches. The later and common Hamilton species, _H. DeKayi_, attained no
extravagant size though frequently large, e. g. the enrolled individual
figured on plate IV (_op. cit._), the largest entire specimen reported,
which is about 9 inches in length; some large fragments indicate that
the animal was sometimes as long as 11 inches.

The size attained by some of the Devonian species of DALMANITES and
their immediate predecessors was marvelous. The pygidium of _D.
micrurus_ figured in the Palæontology of New York, Volume III, page
359 (there given as _D. pleuroptyx_), indicates an individual at least
11 inches in length, and there is reason to believe that the Lower
Helderberg species, _D. nasutus_ and _D. tridens_, attained a size
fully as great. Most remarkable however is the great pygidium of _D.
myrmecophorus_ of the Corniferous limestone, figured upon plate XV of
Volume VII (_op. cit._), which from the restoration there given, made
from careful comparative measurements, would imply an individual 16
inches long.

An interesting feature of the early Devonian trilobitic faunas is
the reappearance of CALYMENE in the Schoharie grit and Corniferous
limestone, a fact which has been duplicated by the recent description
by Dr. OEHLERT of a large species (_C. reperta_), from the lower
Devonian of Saint Malo in Angers. The American Devonian species, _G.
platys_, is not only the latest but the largest known representative
of the genus, and for a group which at its maximum development in
species and individuals in the Silurian, rarely attained considerable
dimensions, the proportions reached by _G. platys_ are especially
noteworthy. The entire individuals on plate 1 of Volume VII of the
Palæontology show this, and the restoration accompanying a very large
pygidium on plate xxv, if accurately drawn, indicates that a length of
upward of eight inches was sometimes attained by the species.

No larger or more extravagantly ornamented trilobite than the
_Terataspis grandis_, HALL, is known. This giant of its race has left
fragments of its test in the Schoharie grit of eastern New York, and
in the commingled Schoharie and Corniferous faunas of the Province
of Ontario. A very complete illustration and discussion of its
different parts, are given in Volume VII of the Palæontology (p. 73,
pls. xvii, xviii, xix), and from these one readily obtains an idea of
the structure of the cephalon, thorax and abdomen, the free cheeks
alone being there unrepresented. There is, however, a very large
free cheek in a fragment of Schoharie grit in the collection of the
American Museum of Natural History, which in all probability belongs
to this species. At the time of the preparation of this volume of the
Palæontology of New York, the original specimen of Mr BILLINGS' species
_Lichas superbus_, was made accessible for study by the kindness of the
Director of the Geological and Natural History Survey of Canada. This
specimen is a portion of the cephalon and a pygidium of _Terataspis
grandis_, lying in juxtaposition on the same block, there being no
doubt of their having belonged to the same animal. From this specimen
it was possible to establish the relative proportions of cephalon
and pygidium in this species, and from the data furnished by all the
material under study, with careful comparative measurements of entire
specimens of LICHAS in the collections of the State Museum, and of
figures of such specimens as have been given by ANGELIN, BARRANDE and
SCHMIDT, the accompanying reproduction of the original size of the
animal has been drawn, its base being the largest and most complete
cephalon figured in the work cited (pl. xvii, fig. 1; xviii, figs. 1,
2).

This restoration gives to the proprietor of this cephalon a length of
nearly 20 inches. The figure does not however do full justice to the
proportions of the animal. In the cephalon which has served as a base
for the restoration the great ovoid central lobe of the glabella has
a length of 2¼ inches. Mr BILLINGS speaks of a specimen of _Lichas
superbus_ in which the length of this lobe was fully 3 inches. If the
increase in size of this part was accompanied by the same relative
increase in the size of the entire animal (and there is no good
reason for assuming the contrary), such a fragment would represent an
individual fully 24 inches in length, a size unsurpassed and unequaled
by any other known trilobite.

With his extravagant armor of defense and aggression, _Terataspis
grandis_ must have been easy lord of his invertebrate domain and no
very palatable morsel for the heavily plated fishes of his day.

In the genera PHACOPS and PROETUS great size was never attained. The
earlier forms of both of these genera were of inconspicuous proportions
and their maximum size was attained in the middle Devonian. An entire
_Phacops rana_ is figured in the Palæontology of New York, Volume VII,
which has a length of 4 inches, and cephala in the Museum collection
indicate an original length of 5 inches, perhaps the greatest size
which has been observed in this genus. PROETUS has a still smaller
habit, that is, its maximum size is never so great, and, probably, the
largest example of the genus recorded is represented by a cephalon of
_Proetus macrocephalus_ from the Hamilton group, which belonged to an
individual fully 3¾ inches in length.


[Illustration: Plate V]


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Transcriber Note

The above article was published as part of the "Tenth Annual Report
of the State Geologist For the Year 1890." (Albany, NY) on pp. 87-90
and Plate V with "Explanation of Plate V" on facing page. It was also
published as part of the "Forty-fourth Annual Report of the Regents for
the Year 1890" (Albany, NY) on pp. 111-114 and Plate V. Unfortunately,
the available scans of these documents DO NOT include the Plate nor
the Explanation pages.