370 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



usually white in Onychomys, mixed with fulvous. Tail with a dorsal 

 stripe of drab extending nearly to the end. Young, smoke-gray, vary- 

 ing to mouse-gray with age. 



Cranial and dental characters. — The 

 skull (fig. 60a) of this species is heavy 

 and has the supraorbital ridges de- 

 veloped as an appreciable beading. 

 Compared with Onychomys pallescens 

 and 0. melanofhrys, it is perceptibly 

 narrower. The interpterygoid fossa 

 appears to be slightly longer. Alto- 

 gether the skulls and teeth of these 

 three forms — longipes (figs. 60?> and c) , 

 jxdlescens, and melano2)hrys— are quite 

 similar, which fact leads to the sup- 

 position that they may ultimately 

 prove to be but geographic races of a 

 common species. The rostrum and nasals of longipes are slightly 

 shorter than in pallescens, the adjoining form on the west. 



Measurements of 8 specimens of Onychomys longipes. 



Fig. 60.— Onychomys longipes. a, Skull; 

 h, Lower molars; 'c, Upper molars. 



