140 CITELLUS. 



Body rather slender; tail either long, moderate, or short, varying 

 greatly in its length among the different species; ears large to rudi- 

 mentary, not tufted; cheek pouches large; skull variable, short and 

 broad like Sciurus, or long and narrow; postorbital processes strong, 

 with a downward direction; antorbital foramen circular, with a well- 

 developed tubercle on outer lower border. 



KEY TO THE SUBGENEKA. 



A. Coronoid process of mandible broad and heavy. PAGE 



a. Nasals equal in length to the premaxillae 

 , . . . Ammospermophilus 141 



b. Nasals not so long as the premaxillae. . .Xerospermophilus 143 



B. Coronoid process of mandible long and slender, 

 a. Nasals longer than the premaxillae. 



a/ Tail short, flat Callospermophilus 147 



b/ Tail long and bushy Otospermophilus 148 



KEY TO THE SPECIES AND SUBSPECIES. 



A. Size small; tail short, narrow. 



a. Upper parts not spotted. 



a/ Tail beneath white on central portion. PAGE 



a." Above grizzled grayish brown and vina- 



ceous C. harrisi 141 



b." Above pale yellowish brown and white. C. h. saxicola 142 



c." Above grizzled gray C. leucurus 142 



d." Above iron gray C. I. peninsula 143 



e." Above grizzled gray and vinaceous . . . . C . inter pres 143 

 b/ Tail not white beneath. 



a." Above grizzled gray and yellowish 



brown C. tereticaudus 1 44 



b." Above fawn color C.I. sonoricnsis 144 



c." Above grizzled yellowish brown and 



black C. perotensis 145 



b. Upper parts spotted. 



a/ Abeve reddish brown C. spilosoma 145 



b/ Above russet brown, white spots bordered 



with dusky C. .<?. microspilotus 145 



c/ Above dark reddish or yellowish brown . . . .C. mexicanus 146 



d/ Above pale reddish brown C. m. parvidens 146 



B. Size large, tail long, bushy. 



a. Tail not over one-fourth total length C. madrensis 147 



b. Tail less than half total length, 

 a/ Tail not annulated. 



