202 BULLETIISr 144, UNITED STATES NATIONAL MUSEUM 



Fur aTid color. — The fur is rather thin, of only medium length 

 (4 or 5 mm. at the center of the back), and except imder the wing, 

 it extends very little on to the membranes. Its color is characteristic. 

 The basal three-fourths or thereabouts of the hairs is a uniform light 

 chocolate, nearly " Rood's brown " (Ridgway, 1912) ; the tips of the 

 hairs above are glistening pale buff giving a finely peppered or 

 frosted effect anteriorly and forming, in fresh pelage, a noticeable 

 wash posteriorly. Below, the bases of the hairs are of the same 

 light chocolate, but the terminal portion is clear whitish cartridge 

 producing a contrasted pale ventral surface. Posteriorly the pale 

 tips increase in length until at the edges of the abdomen the hairs 

 are entirely buff. The interramial area is uniformly dark chocolate 

 brown. The membranes are light brownish becoming distinctly pale 

 between the humerus and the legs. The interfemoral membrane is 

 also pale. In immature specimens the dark portions of the fur are 

 nearly sooty, but the pale tips are characteristic. The membranes 

 also are darker, blackish brown. 



Skull. — The skull somewhat resembles that of Myotis chiloensis, 

 with which it agrees in general size, but differs from that of all 

 the known South American members of the genus in the relatively 

 large, noticeably globular, smoothly rounded form of the brain case, 

 and the relatively short, weak rostnini. (PI. 1, p. 7, fig. 8.) The 

 sagittal crest, when present, is never anything more than a low, 

 inconspicuous ridge. 



Teeth. — There appear to be no tangible structural characters by 

 which the teeth can be distinguished from those of Myotis chiloensirS, 

 except that the transverse diameter of the crown of the upper molars 

 tends to be less in proportion to the diameter along the alveolar line 

 than in M. cMloensis or any of the other known South American 

 species. The full complement of secondary ridges and cusps is 

 present in the upper molars. Cingulum rather weakly developed. 

 Crown area of cheek teeth unusually small in comparison with area 

 of intervening palate, this feature alone sufficient to distinguish the 

 species from any of the members of the genus with which it might 

 be confused. 



Measurements. — For measurements see tables, pages 204 and 205. 



SpeciTnens examined. — Total number 98, from the following 

 localities : 



ARGENTINA: Buenos Aires, 1 ale. (B. M.) ; Corrientes Province, Goj-a, 

 2 skins (B. M.) ; La Pampa Territory, Rio Colorado, 1 ale. (B. M.). 



BOLIVIA: Rosario, 1 ale. (U.S.N.M.). 



BRAZIL: Amazonas Provinee, Ega (=Teffe), 1 skin, immature (B. M.) ; 

 Manaos, 1 skin (U.S.N.M.) ; Rio Grande do Sul, 1 ale. (B. M.). 



BRITISH GUIANA: southern part, Ireng Valley, 1 ale. (B. M.). 



COLOMBIA: Barbacoas, 2 skins (A. M. N. II.); Chooo region, 2 ale. 

 (B. M.). 



