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.