174 I' iiici rsity of California Publications in Zoology [Vol. 10 



Its range is possibly determined by the presence of alluvial soil 

 at the mouths of the canons whose streams vanish into the desert 

 below. 



Thomomys albatus is apparently confined to that portion of 



the Colorado desert occupied by the delta of the Colorado River 

 and hence having' fine alluvial soil, and further, to thai portion 

 of the delta region lying west of the main channel of the 

 Colorado River, and above the reach of recent overflow. 



Albatus is, judging from descriptive literature as well as 

 from all available material, the whitest gopher known, and this 

 peculiarity is quite as pronounced in very small young as in 

 adults. This extreme pallor in an animal of subterranean habits, 

 one which is seldom exposed to the light, is difficull of explana- 

 tion, when it is borne in mind that the gophers of the coast belt 

 of California are very dark colored. The soil of the habitat of 

 nl lull us is usually perceptibly moist, not conspicuously less so 

 than that in the San Diegan district. It would appear that in this 

 case relative humidity could not so well be called into account, 

 nor intense light, as in the cases of mammals foraging above 

 ground. Yet this gopher is whiter than any other mammal of 

 the Imperial region, though all are pale-colored as compared with 

 relatives in neighboring zoogeographic areas. 



Thomomys chrysonotus, new species 

 Ehrenberg Gopher 



Type: Male young adult ; no. 10617, Mus. Vert. Zool.; Ehren- 

 berg, Yuma County. Arizona: March 27, 1910; collected by P. 

 Stephens ; original no. 2540. 



Diagnostic Characters: Size .small; colors pale: similar to 

 Thomomys perpallidus, but dorsal coloration with a distinctly 

 golden cast, cars very small, and skull in proportion to size much 

 heavier. 



Description of Type: Coloration ochraceous-buff above, with 

 a tinge of ochraceous-rufous or golden mid-dorsally ; facial region 

 the same, slightly obscured with dusky around the nose; 

 beneath whitish with much plumbeous of the bases of the hairs 

 showing through; feet and tail white; dorsal color rather 



