1912] Grinnell: Two Pocket Gophers of the Colorado River \1'?> 



posteriorly; zygomata widely spreading; zygomatic breadth 

 greatest anteriorly, that is, across maxillary portion; this por- 

 tion also projecting ventro-laterally, so that there is conspicu- 

 ously deep ventral excavation of the anterior zygomatic root as 

 viewed from in front (shown also in slight degree in ventral 

 view, fig. 3, pi. 5) ; auditory bullae relatively depressed. 



Measurements : See table, p." 176. 



Distribution: There are in the Museum, twenty-three speci- 

 mens of this form, as follows, all from Imperial County : Colorado 

 River bottom near Pilot Knob. 8; Salt Creek. 8; southern side 

 of Salton Sea, 6; Carrizo Creek, 1. 



Remarks: In the original description of Thomomys /<< r- 

 paUidus (C. H. Merriam, 1886, p. 588), no exact type locality 

 was designated; but Stephens (1906, p. 138) gives it as Palm 

 Springs, he having collected the material upon which .Merriam 

 based his description. Vernon Bailey informs me that the 

 Biological Survey considers Palm Springs, once called Agua 

 Caliente, as the type locality. Hence I use the series in the 

 Museum from that exact place as representing perpallidus in 

 the most restricted sense. A perusal of the literature shows that, 

 as is usual in similar cases, the earliest name for a pale-colored 

 gopher has at different times been attached to specimens from a 

 large area around the Colorado desert, even to northeastern 

 Arizona. But as material has accumulated, various forms have 

 been cut out from the periphery, with successive studies more and 

 more narrowing the area of application of the name perpallidus. 



My present study is a still further refinement, wholly justifi- 

 able with the new material in hand. The material as yet avail- 

 able, is, however, insufficient to establish whether or not the 

 ranges of the different recognized forms are sharply defined or 

 whether the distribution is practically continuous, and is accom- 

 panied by intergradation in characters. 



Two conclusions, however, seem probable: one is, that per- 

 pallidus as redefined does not occur east of the Colorado River; 

 the other, that on the lower parts of the Colorado desert it is 

 replaced by the form here named albatus. It may even be prob- 

 able that perpallidus is restricted to a narrow belt along the 

 eastern base of the mountains lying west of the Colorado desert. 



