468 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



specimens relaxed by Miller (1928, p. 206). Actually the wing is 

 attached to the foot at the base of the toes in simus as in most other 

 My otis. The calcaral keel, described as practically absent, indeed 

 is absent in a few specimens, but as a rule it is well developed. The 

 width of the rostrum and crowding of the maxillary tooth row are 

 geographically variable. Coloration and length of fur are seasonably 

 variable. 



Thus, Myotis simus is not so strikingly differentiated from other 

 species of Myotis as Thomas and Miller supposed, and there is little 

 basis for the subgeneric name Hesperomyotis proposed for it by 

 Cabrera (1958, p. 103). 



The Panamanian specimens were caught in mist nets set over 

 streams in a lowland semideciduous forest and a mountain forest, and 

 at the edge of a clearing in a mountain forest. 



Specimens examined: M. s. riparius: Panama: Boca de Paya, 

 Darien, 1, USNM; Cerro Azul, 2,100 ft., 1, USNM; Tacarcuna Village, 

 3,200 ft., Rio Pucro, Darien, 4, USNM. M. s. simus: Brazil: Auara 

 Igarape, Rio Madeira, 7, AMNH; Cacao Pereira Igarape, Rio Negro, 

 8, AMNH; Igarape Amorin, Rio Tapajoz, 3, AMNH; Rosarinho, Rio 

 Madeira, 4, AMNH; Villa Bella Imperatriz, South bank of Rio 

 Amazonas, 14, AMNH. Ecuador: Boca de Rio Curaray, 16, AMNH, 

 2, USNM. Peru: Apayacu, Rio Amazonas, 4, AMNH; Orosa, Rio 

 Amazonas, 3, AMNH; Panya, Boca de Rio Topaya, Ucayali, 1, 

 AMNH; Rio Pisqui, Ucayali, 1, AMNH; Sarayacu, Rio Ucayali, 12, 

 topo types of simus, AMNH. 



Lasiurus castaneus, new species 



Holotype: USNM 310263, adult female (with 2 embryos, 13 mm. 

 crown rump), skin and skull, collected March 6, 1959, by Charles O. 

 Handley, Jr., and B. R. Feinstein, Tacarcuna Village, 3,200 ft., Rio 

 Pucro, Darien, Panama, original number 5445. 



Distribution: Known only from the type locality, where a single 

 specimen was taken in a mist net over a stream in a mountain forest. 



Description: Dorsum deep chestnut (between Morocco Red and 

 Chestnut), shading on rump, interfemoral membrane, and feet to 

 mahoganj r (between Maroon and Claret Brown); median band of 

 individual dorsal hairs Cinnamon-Rufous; individual hairs tricolored, 

 with individual bands (black-amber-chestnut) about equal in extent; 

 face and muzzle, entirely black; underparts blackish brown with only 

 scattered buff-tipped hairs except on collar; throat not differentiated 

 from remainder of underparts in color; hairs surrounding white 

 humeral spot black tipped; ears, wings, membranes, paid lips entirely 

 blackish. Distal fourth of interfemoral membrane naked; auricle 

 and antitragus relatively large. M 3 much reduced, second com- 



