UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. 10, No. 8, pp. 171-178, pi. 5 June 7, 1912 



THE TWO POCKET GOPHERS OF THE 



REGION CONTIGUOUS TO THE LOWER 



COLORADO RIVER, IN CALIFORNIA 



AND ARIZONA 



BY 



JOSEPH GRINNELL 



(Contribution from the Museum of Vertebrate Zoology of the University of California) 



The explorations carried on in 1910 along the lower Colorado 

 River from Needles to the Mexican line produced large collec- 

 tions of mammals, which, however, included but few specimens 

 of the genus Thomomys. Only one individual was obtained on 

 the Arizona side, and on the California side none was found 

 above the apex of the delta region below Yuma. 



An attempt to fix the specific status of these gophers resulted 

 in a fair degree of certainty that distinct forms were represented 

 on the two sides of the river, and that the specimens from the 

 California side were identical with our material already a1 hand 

 from several points in the Imperial Valley. 



It happened, however, that the Museum contained but two 

 specimens of gopher from the type locality of Thomomys per- 

 pallidus C. H. Merriam, described from specimens obtained at 

 Palm Springs, at the extreme northwestern end of the Colorado 

 desert. Correspondence elicited the information that the material 

 in the Biological Survey collection was also unsatisfactory for 

 comparison. And as a proper knowledge of the characters and 

 variation in the first described species of the general area, 

 namely, Thomomys perpallidus, seemed an essential basis for 

 treatment of the other species from the desert regions of the 



