240 GNAWING ANIMALS 



CHEEK-POUCH MICE AND RATS 



Family Heteromyidae 



This is strictly a Family of the West and Southwest, its 

 members being found only west of Arkansas, Iowa, and Min- 

 nesota. It does not contain the pocket gophers. Many of 

 its twenty-six species are desert dwellers, even inhabiting 

 Death Valley, California. All its members are distinguished 

 from other North American animals (except the jumping 

 mouse and pocket gopher) by the presence of a large and 

 very serviceable hair-lined pouch in the skin of each cheek. 

 Barring the two exceptions noted, this character alone is suf- 

 ficient for the recognition of any American member of this 

 Family. 



As clearly shown in the full-page diagram, this family 

 may be divided into two subfamilies, an arrangement which 

 is very convenient and helpful. The first we must call the 

 Pocket Mouse subfamily and its leading genus {Per-og- 

 na'thus) contains twenty-six full species, and fifteen subspe- 

 cies. All are distinguished by the following characters : head 

 large; body slender and graceful; hind legs long, and fitted 

 for jumping; tail long; large external cheek pouches, hairy 

 inside, and not connected with the interior of the mouth; hair 

 smooth and compact, sometimes intermingled with spines. 

 These mice are quick and active in movement, and some 

 species leap with considerable power. 



Since 1839 the Typical Pocket Mouse^ has been de- 

 scribed again and again, but none of its describers have 



^ Perognathus fasciatiLS. 



