668 THE MONTHLY BULLETIN. 



The two specimens in the Museum of Vertebrate Zoology were trapped 

 on the first two specified dates, in 1918, on the hillsides immediately 

 west of Little Lake. They were daytime-taken in oat-baited rat-traps 

 set beneath creasote bushes on gravelly ground. In spite of diligent 

 search by the collectors everywhere in the neighborhood, not one of this 

 species was seen alive. No information is available to us in regard to 

 either behavior or food. 



This ground squirrel is altogether distinct from Citellus tereticaudus. 

 There is no indication of intergradation with that species, as stated by 

 Elliot (1904, p. 291). In fact, the animals reported by that author 

 from Daggett were all probably in reality tereticaudus, which species is 

 known to us to be present at Daggett. The tail of mohavensis is always 

 much shorter and more broadly haired than in tereticaudus, the claws 

 are stouter, the cheeks are brownish instead of white, the under side of 

 the tail is white, instead of buffy with brown mottlings toward the end, 

 the quantity of winter pelage is greater, and the general tone of colora- 

 tion is always decidedly dark. 



The fact that the under side of the tail is white, as in the Antelope 

 Ground Squirrel, leads us to suspect some such special habit of display- 

 ing this member as is possessed by the latter animal. But this is mere 

 speculation. The relationships of mohavensis as indicated by structural 

 features are thought to lie rather with Citellus than with Ammosper- 

 mophilus. 



YUMA ROUND-TAILED GROUND SQUIRREL. 

 Citellus tereticaudus tereticaudus (Baird). 



PLATE IV. 



Other names. — Round-tailed Spermophile; Yuma Ground Squirrel; Mohave 

 Desert Ground Squirrel, part ; Spermophilus tereticaudus ; Xerospermophilus tereti- 

 caudus ; Citellus tereticaudus mohavensis, part. 1 



Field characters. — A small ground squirrel, of slender build, and of pale brown 

 color (no stripes or other markings) ; tail long and slender, not broadly haired; ears 

 very small, mere rims ; length of body without tail about 6 inches, with tail about 

 3f inches more. 



Description. — Adult in winter pelage : Whole upper surface from nose to and 

 including tail, light pinkish cinnamon in general tone; individual hairs lead-colored 

 at extreme bases, then dull white, then pinkish cinnamon, and with tipping of white. 

 Eyelids and whole lower surface to root of tail, white; side of head and neck 

 including ear dull white ; whiskers black ; hairs of belly lead-colored at extreme bases. 

 Upper surfaces of feet dull buffy white; claws dark brown basally, becoming horn- 

 color at tips ; soles of feet haired save for under sides of toes. Tail cylindrical in 

 shape, a little more heavily haired toward end than at base ; under side dull buff, with 

 black mottlings in fine pattern toward end ; above like back on basal half, becoming 

 black and buff mottled toward end ; hairs at tip of tail brown at their bases, then buff, 

 then broadly black, and with white ends. 



Adult in summer pelage: Coat short and harsh as compared with winter coat; 

 color above brighter pinkish cinnamon. Otherwise as in winter, but the tail, which 

 apparently does not molt, pale brown and still slenderer, due to the fading out of the 

 dark colors and to the wear and consequent shortening of the hairs. 



Color variations. — Young partly grown are colored like summer adults, but the 

 pelage is not quite so harsh and on the under surface is so sparse as to allow 

 the bare skin to show through in places. There are two molts in the adults each year 



76 



