Comparative Evolution of Biomes 



311 



Fig. 135. Distribution of the ground squirrels of the genus CiteUiis. The 

 northern hatched area is the North American range of the Holarctic species 

 C. itndulatus, the lower area the combined ranges of the other 19 Nearctic 

 species. (Adapted from Burt and Grossenheider and from Rausch.) 



