Prairie Dogs 
149 
postorbital processes; dentition, i. { ; pm. f;m.fX2=22; anterior 
premolar large; molars with 3, not 2, transverse grooves on their 
crowns; molar series converging behind. 
This genus containing the Prairie Dogs is confined to 
North America west of the Mississippi Valley; seven species 
are to be found in Elliot's Check-list, three of which inhabit 
Colorado, and can be distinguished as follows: 
Key of the Species 
A. Larger, total length over 14.0 ; tail with apical third black. 
C. ludovicianus, p. 150 
B. Smaller, total length less than 14.0; tail with apical half 
mixed black and white and tipped with white; head 
darker than the back; no dark eyebrow. 
C. gunnisoni, p. 153 
C. Size as in last; tail with apical | white; head same color as 
back, a distinct dark stripe over the eye and a patch 
below. C. leucurus, p. 154 
FIG. 51. PLAINS PRAIRIE DOG, Cynomys ludovicianus 
Skull showing dentition x i| 
