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                  A New Bat (Genus Myotis) From Mexico

                                   BY

                 WALTER W. DALQUEST and E. RAYMOND HALL


                   University of Kansas Publications
                       Museum of Natural History


                     Volume 1, No. 12, pp. 237-244
                           December 10, 1947


                          UNIVERSITY OF KANSAS
                                LAWRENCE
                                  1947



      UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

    Editors: E. Raymond Hall, Chairman, H. H. Lane, Edward H. Taylor

                     Volume 1, No. 12, pp. 237-244
                           December 10, 1947


                          UNIVERSITY OF KANSAS
                            Lawrence, Kansas


                               PRINTED BY
                    FERD VOILAND, JR., STATE PRINTER
                             TOPEKA, KANSAS
                                  1947

                                22-1402




                A New Bat (Genus Myotis) From Mexico[1]

                                   By

                 WALTER W. DALQUEST AND E. RAYMOND HALL


While one of us (Dalquest) was in a dugout canoe that was being paddled
up a small unnamed tributary of the Rio Coatzacoalcos, through dense
jungle, he grasped a decayed and termite damaged tree-trunk projecting
approximately three feet above the surface of the water to steady the
canoe. At that instant two bats were detected in one of the many small
holes in the trunk, which was eight to nine inches in diameter. It was a
simple matter to enlarge the hole and extract the animals. Superficially
they resembled silvery-haired bats (_Lasionycteris_) but their naked
interfemoral membranes and other features suggested that they belonged
to the genus _Myotis_. Subsequently, study in the laboratory showed this
to be the fact and revealed also that they are of an heretofore unnamed
species which may be known as:


                    #Myotis argentatus#, new species

    _Type._--Male, adult, skin with skull, No. 19228, Mus. Nat.
    Hist., Univ. Kansas; 14 kilometers southwest of Coatzocoalcos,
    100 feet elevation, Veracruz, Mexico; 2 February 1947; obtained
    by Walter W. Dalquest; original No. 7052.

    _Range._--Known only from the type locality.

    _Diagnosis._--Size medium for the genus (see measurements), tail
    short; foot long; ears and membranes black; pelage long (maximum
    length on middle of back 9 mm.) and black; upper parts with
    overhairs tipped with whitish especially on rump; underparts
    from posterior part of thorax posteriorly with all of the hairs
    tipped with this same whitish color; skull with preorbital part
    small in relation to brain case; teeth small in relation to
    total area of palate; brain case much inflated; ventral margin
    of foramen magnum evenly rounded.

    _Comparison._--From _Myotis albescens_ (E. Geffroy) known to us
    by specimens in the United States National Museum from Paraguay
    (Tacural), Panama (Tabernilla), and Nicaragua (Prinzapolca R.
    and Escondido R.), _argentatus_ differs in: Body and foot
    longer; tail relatively shorter (57 and 58% of length of head
    and body versus 76 (62-83)% in _albescens_); tibia shorter;
    pelage longer, and black instead of brown; silver tipping of fur
    on hinder back markedly more conspicuous; precranial part of
    skull, when viewed from above, larger in relation to brain case;
    postorbital constriction less abrupt, that is to say, skull
    "longer-waisted"; occlusal surfaces of teeth of equal area and
    therefore occupying a relatively smaller percentage of total
    area of palatal surface; ventral margin of foramen magnum less
    deeply indented; ventrally prominent part of basioccipital twice
    as wide.

_Remarks._--The relatively slight wear on the teeth of the female of _M.
argentatus_ and the large ends on the bones of the wings indicate that
it is immature. Its measurements, recorded below, average smaller than
those of the adult holotype, a male, and the silvery tipping on the
upper parts is almost lacking from the pelage which is shorter than in
the holotype.

    [Illustration: FIGS. 1-6. _Myotis_. From left to right, dorsal,
    lateral and ventral views. All × 2.

    FIGS. 1-3. _Myotis argentatus_, no. 19228, Univ. Kan. Mus. Nat.
    Hist., type.

    FIGS. 4-6. _Myotis albescens_, no. 105664, [F], U. S. Nat. Mus.,
    from Tacuaral, Paraguay; obtained on November 13, 1900, by Wm.
    T. Foster, orig. no. 128.]

Among at least American kinds of _Myotis_, _argentatus_ is extreme in
small area of occlusal surface of the upper molariform teeth in relation
to the total area of the palatal surface of the skull. _M. albescens_
previously was regarded as extreme in this feature. The distance across
the third upper molars, from the outside of one tooth to the outside of
the other, is 5.5 mm. in the holotype of _argentatus_ and 5.4 mm. in a
specimen of corresponding age and sex of _albescens_. The distance
between the third upper molars, from the lingual side of one tooth to
the lingual side of the other, is 2.9 mm. in _argentatus_ and 2.8 mm. in
_albescens_.

In each of our two specimens there is no sagittal crest but instead a
low ridge one millimeter wide which marks the space between the margins
of the two temporal muscles.

Allusion already has been made to the resemblance of the newly named
_Myotis argentatus_ to the silvery-haired bat, _Lasionycteris
noctivagans_ (LeConte). The whitish tips of the hairs are slightly more
yellowish in _argentatus_ but the difference is so slight as to be
detected by only the most careful comparison. The remainder of the
pelage in _argentatus_ is black as in the darkest individuals of
_Lasionycteris_.

Among named kinds of the genus _Myotis_, the species _argentatus_ most
closely resembles _Myotis albescens_ which, up to now has been recorded
from as far south as Argentina, in South America, and as far north as
Nicaragua, in Central America (Miller and Allen, Bull. U. S. Nat. Mus.,
144:202, 203, 1928). The differences detected between the two species
are indicated above in the paragraph of comparisons and some other
differences can be detected by comparing measurements given below with
those of _M. albescens_ as recorded by Miller and Allen (_op. cit._:
204-205). In initial comparisons with _albescens_, only Paraguayan
specimens were employed. It was felt that specimens of _albescens_ from
the northernmost localities of occurrence might more closely resemble
_argentatus_. Accordingly, we appealed a second time to Dr. A. R.
Kellogg for comparative material and he lent us the specimens
(alcoholics with skulls separate) in the U. S. National Museum from
Central America. These also differ from our newly named bat in the same
fashion as do the South American specimens. Further, the number and
magnitude of the differences between _albescens_ and _argentatus_
greatly exceed any that can be pointed to between the American
subspecies of any other one full species of the genus _Myotis_. Full
specific, rather than mere subspecific, status, therefore, is suggested
for the bat here named _Myotis argentatus_.

    _Measurements._--The adult, male type, and the immature female
    specimen measure, respectively, as follows: Head and body, 55,
    51 mm.; tail, 32, 29; tibia, 13.7, 13.2; foot, 8, 9; forearm,
    33.0, 34.5; thumb, 5.8, 5.7; third metacarpal, 32.2, 30.5;
    fifth metacarpal, 31.5, 30.3; greatest length of skull, 14.5,
    14.0; condylobasal length, 13.8, 13.0; zygomatic breadth, 9.1,
    9.0; interorbital constriction, 4.3, 4.0; breadth of brain case,
    7.5, 7.4; occipital depth, 5.7, 5.7; mandible, 10.5, 10.0;
    maxillary tooth row, 5.3, 5.0; maxillary breadth at M3, 5.5,
    5.7; mandibular tooth row, 5.6, 5.3.

    _Specimens examined._--Two, from the type locality.

  _Transmitted October 20, 1947._


                                FOOTNOTE

  [1] Assistance with field work is acknowledged from the University
      of Kansas Endowment Association.