GEOGRAPHIC DISTRIBUTION. 



29 



is clearly of Sonoran origin aud readies its highest development on the 

 southern part of the table-land of Mexico. The great majority of the 

 species inhabit the upper and lower Sonoran zones, though a few spe- 

 cially modified forms range upward on favorable mountain sides through 

 the Transition and even into the lower edge of the Boreal zone. On 

 the other hand, two species inhabit the Tropical belt of Mexico. 



The genus Thomomys has by far the most extended range of any of 

 the three, inhabiting suitable localities from the Valley of Mexico and 

 Mount Orizaba northward to British Columbia and the North Sas- 

 katchewan, and from the Pacific Coast eastward to the Great Plains. 

 It is represented by numerous species. 



Fig. C. — Geographic distribution of Pocket Gophers by genera. 



The genus Cratoyeomys inhabits the Great Plains of the United States 

 from the Arkansas Biver in eastern Colorado southward, and extends 

 far into Mexico (see fig. 6 and map 1, H). 



The genus Geomys inhabits a broad belt across the middle part of 

 the United States from the Bed Biver Valley in northwestern Minne- 

 sota and northeastern North Dakota southward to the Mexican bound- 

 ary along the Bio Grande; and also the southern half of Alabama 

 and Georgia and the northern half of Florida. It does not occur west 

 of eastern Wyoming, east central Colorado, and the Bio Grande Valley 

 in New Mexico (see fig. 6 and map 1). 



THE SPECIES OF GEOMYS. 



The Georgia Gopher (Geomys tuza), a rather large cinnamon-brown 

 species, inhabits the pine barrens of eastern Georgia, where it is 



