172 University of California Publications in Zoology [Vol. in 



southwest, it became necessary for the time being to defer action 

 upon the Colorado River material. 



In February. 1!)12. the writer was fortunately able to pay 

 a brief visit to Palm Springs in the interests of the Museum, and 

 he succeeded in securing a quite satisfactory series of thirty-eight 

 specimens of Thomomys perpallidus. Twelve of these arc com- 

 parable males. The entire material provides the requisite basis 

 for comparative treatment of the forms from the Colorado River 

 region, and proves them to be distinct one from the other, and 

 both different from perpallidus. 



Thomomys albatus, new species 

 Imperial Valley Gopher 



Tvpe: Male adult; no. 10618, Mus. Vert. Zool.; California 

 side of the lower Colorado River at the old Ilanlon Ranch, near 

 Pilot Knob, Imperial County; May 7. 1!)1(); collected by .(. 

 Dixon; original no. 1396. 



Diagnostic Chabactebs: As compared with Thomomys per- 

 pallidus, colors extremely pale; size large; tail long; feet broad; 

 zygomata most widely spreading in maxillary portion, that is, 

 anteriorly. 



Description of Tvpe : Coloration very pale cream buff above 

 (very much whiter than in T. perpallidus, and in T. perpes of 

 the Mohave Desert), becoming dusky around nose and mouth; 

 a small patch of slaty hairs beneath ears; tail and feet scantily 

 clothed with whitish hairs; inside of ears with fine slaty hairs, 

 but outside with coarser hairs of the color of back; vibrissae 

 whitish; lower surface white, tinged with straw yellow on throat, 

 fore legs, and anal region : the white of the lower surface extends 

 high on the sides, blending gradually with the cream buff of the 

 mid-dorsal region; hairs of the dorsal region pale plumbeous at 

 base. There are evidences of molt; the newly appearing hairs 

 are faintly dusky-tipped, but there is no evidence of diverse 

 seasonal coloration. 



Skull (as compared with T. perpallidus and T. perpes) large 

 (see table, p. 176, and plate 5) ; rostrum heavy; incisors massive 

 and more incurved; nasals and premaxillary tongues broad 



