322 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



A specimen (No 141) differs from that just described (142) in being larger, and having the 

 light spots very indistinct and scarcely appreciable, even posteriorly. It is probable that the 

 spots are most distinct in younger specimens. 



The differences between this species and S. mexicanus can be readily expressed. The ears are 

 decidedly shorter and more rudimentary ; the tail is narrower, much less bushy, particularly 

 on the basal portion ; the claws are larger and blacker, the thumb claw larger, the soles more 

 hairy. The color is brighter, being strongly reddish brown or cinnamon ; the spots are not 

 arranged serially, and are more indistinct, their posterior portion only, black instead of the ante 

 rior likewise this being due to an essential difference in the colors of the hair occupying the 

 spots. In S. mexicanus they are black beyond the lead-colored base, with a subterminal light 

 portion and black tip ; in the present they are reddish brown beyond the basal color, then light- 

 colored, and tipped only with black. The basal color, generally, is much deeper. The hairs 

 on the sides of the extremity of the tail have one black central space, with a narrower base, and 

 tip of lighter tints, while those at the extreme tip are black to the base, with light tips ; in S. 

 mexicanus all these hairs have two black rings, both at sides and tip, the light portion being 

 uniform throughout. 



It is true that the young animals are more distinctly spotted than the adults, but they may 

 always be distinguished from small specimens of S. mexicanus by the fact that the spots are not 

 arranged in regular linear series, and are not distinct on the anterior half of the body. The 

 ground color is also always more chestnut in tint. 



Differences of equal value are discernible in the skulls ; that of the present species being 

 shorter, broader, the orbits larger, the muzzle blunter, &c. 



S. toivnsendii differs in having the ground color above darker, and a much shorter tail. 

 This species was first described from specimens collected on the western coast of Mexico. The 

 vicinity of El Paso seems to be its eastern, and the Gila its northern limit. It was erroneously 

 considered to be the young of Spermophilus mexicanus by Audubon and Bachman. 



List of specimens. 



Skull 1.54 + .98 inch ; mamma: 10. 



Skull 1.45+ .97 inch. 



