1912] driii iidh Two Pocket Gophers of the Colorado River 175 



abruptly defined along sides against white of lower surface; 

 dorsal pelage at base deep plumbeous; vibrissae whitish; ears 

 thinly clad with fine slaty hairs, but not surrounded by dusky 

 patch. 



Skull (as compared with T. perpallidus and T. albatus) small, 

 but relatively massive (see table, p. 17ti. and plate 5); rostrum 

 short and broad, broadest in its middle portion ; incisors heavy 

 and incurved; posterior ends of premaxillary tongues reaching 

 scarcely beyond nasals; zygomata not spreading conspicuously, 

 nor prominently angled; jugal bars approaching one another 

 anteriorly, that is, zygomatic width greatest posteriorly; inter- 

 orbital constriction very wide ; auditory bullae relatively much 

 inflated. 



Measurements: Sec table, p. 17ti. 



Distribution: Type and only specimen from Ehrenberg, 

 Yuma County, Arizona. 



Remarks : I sent the type specimen to Vernon Bailey, of the 

 United States Biological Survey, who marked it tentatively 

 Thomomys perpallidus. Comparison, however, of this specimen 

 with the topotype series of perpallidus now available, discloses 

 differences which fall far outside of the range of individual 

 variations in perpallidus. The distinct golden color of chryso- 

 notus, even brighter than in T. perpes, together with certain 

 cranial peculiarities, lead me to suggest its near affinities, no1 

 with perpallidus or albatus, but with forms to the east and north. 



