MAMMALS 319 



T. m. mazama (Merr.)- Color darker and richer: Cascade and Sis- 

 kiyou Mountains; southward to the Trinity Mountains; northward 

 to the Columbia. 



T. m. pinetorum Merr. Nose and cheeks conspicuously gray: 

 mountains on the west side of Sacramento Valley. 



T. fiiscus (Merr.) . Color light brown ; length 203 mm. ; tail 70 mm. ; 

 hind foot 27 mm.; mammae 4 pairs: Wyoming to Washington and 

 northward into Canada; 5 subspecies. 



Subspecies of T. fusciis 



T. f. fiiscHs (Merr.). Western Montana and Wyoming, northern 

 and central Idaho, eastern Oregon and Washington, British Columbia. 



T. j. saturatus Bailey. Size larger; color darker: higher parts of the 

 Coeur d'Alene Mountains. 



T. hes perns Merr. Color dark rich auburn; length 210 mm.; tail 60 

 mm.; hind foot 24 mm.: coast region of northwestern Oregon. 



Family 3. Heteromyidae. — Small, slender rodents with a long 

 tail and with a pair of cheek-pouches, which are lined with fur on the 

 inside and open at the side of the mouth on each cheek; eyes and ears 

 u.sually large; fur harsh in many species, with numerous bristles or 

 spines: 6 genera and about 100 species, all in America, mostly in more or 

 less arid regions of the western States and Mexico. 



Key to the United States Genera of Heteromyidae 



ai Progression by walking i. Perognathus. 



ao Progression by leaping. 



bi Tail with a terminal pencil 2. Dipodomys. 



bo Tail without terminal pencil 3. Mkrodipodops. 



I. Perognathus Wied. Pocket mice (Fig. 176). Body slender and 

 murine; tail at least as long or nearly as long as the rest of the body; 

 ears small; legs and feet long; dentition i/i, 0/0, 1/1,3/3; molars rooted 

 and tuberculate; upper incisors strongly sulcate; hair harsh in some 

 species and soft in others: many species, all in North America; about 25 

 species and very many subspecies in the United States, all west of the 

 Mississippi; nocturnal, burrowing animals, dwelling on plains and 

 deserts and feeding on seeds; several litters of young raised annually, 

 numbering from 2 to 8 each. 



P. fasciatus Wied. Color oHvaceous; pure white below; fur soft; 

 soles of feet hairy; length 134 mm.; tail 64 mm.; hind foot 17 mm.: 

 eastern Montana and Wyoming and western Dakota; Upper Sonoran 

 and Transition zones. 



