106 Proceedings of the Biological Society of Washington. 



tone; C. t. chlorus Elliot, of the northwestern arm of the Colorado 

 Desert, in Riverside County, California, is avellaneous; C. t. tereti- 

 caudus (Baird), of the Colorado and Mohave deserts, in Imperial, 

 extreme eastern Riverside, and San Bernardino counties, California, is 

 light pinkish cinnamon; while C. t. arizonae, of southwestern Arizona, 

 is deep pinkish cinnamon. The color-terms here used are taken from 

 Ridgway's " Color Standards and Color Nomenclature," 1912. 



That the last two specified forms exist, and that the Colorado River is 

 the dividing line between them, was evidently believed by Mearns, who 

 says of Citellus tereticaudus (Bull. 56, U. S. Nat. Mus., 1907, pp. 336- 

 337): "Specimens from the Tule and Yuma deserts, to the eastward of 

 the Colorado River, are more reddish than those taken at the same season 

 on the western part of the Colorado Desert." The present writer (Grin- 

 nell, Univ. Calif. Publ. Zool., vol. 12, 1914, pp. 224-225) went into the 

 matter more in detail, showing that the characters hold right up to the 

 river, but he did not at that time have at his disposal sufficient material 

 to justify separation of the races by name. 



The type-locality of Citellus tereticaudus, according to Mearns ( loc. cit. ), 

 is "Old Fort Yuma, San Diego [now Imperial] County, California (on 

 the right bank of the Colorado River, opposite the mouth of the Gila 

 River and the present town of Yuma, Arizona)." 



