MAMMALS 337 



Ci Cheek-pouches absent; tail very long; squirrels. . . i. Sciurus. 

 C2 Cheek-pouches present; tail moderate. 



di Thumb with well-developed nail; chipmunks. 



ei Premolars i/i ; eastern chipmimks 2. Tamias. 



Co Premolars 2/1; western chipmunks (Fig. 



181) 3. Eutamias. 



d-2. Thumb with rudimentary nail (Fig. 182); 

 ground squirrels, 

 ei Back broadly striped. 



fi Head and neck with a golden mantle. . . .4. Callospermo philiis . 



£2 Head and neck colored like back 5. Ammospermophilus. 



62 Back with narrow stripes or mottled or 



grizzled; gophers 6. Citellus. 



b2 Body stout and heavy; tail short; cheek-pouches 

 shallow. 



Ci Color uniform; prairie dogs 7. Cynomys. 



Co Color not uniform; woodchucks 8. Marmota. 



ao Sides of body with furred membrane (flying squirrels).. .9. Sciuropterus. 



I. Sciurus L. Body slender; tail long and bushy, the hairs being 

 longest on the sides; ears and eyes large; thumb rudimentary; dentition 

 I /i, 0/0, I /i or 2 /i, 3 /3 : over 100 species; cosmopohtan, excepting the 

 Australian region; 10 species and numerous subspecies in the United 

 States; about 30 species in Mexico and Central America; arboreal and 

 mostly diurnal rodents which feed on seeds, nuts and buds, and often 

 on young birds, bird-eggs and insects, and which build their nests in 

 trees; they probably do not usually hibernate, and usually lay up stores 

 of food. 



Key to the Species of Sciurus in the United States 



ai Upper premolars 2 in number, making 5 grinders on each side in 

 upper jaw (Fig. 179). 

 bi Size small; hind foot less than 55 mm. long; color red. 

 Ci In the eastern, central and Rocky Mountain States. 



di In the northeastern, north-central and Rocky Moun- 

 tain States; common red squirrel S. hudsonicus. 



do In the central Rockies and southwestern States S. fremonti. 



02 On the Pacific slope S. douglasi. 



hi Size large; hind foot more than 60 mm. long; color gray, 

 sometimes black. 

 Ci Ears not tufted. 



di In the eastern and central States; common gray 



squirrel S. carolinensis. 



d2 On the Pacific slope 5. griseus. 



C2 Ears tufted with long black hairs. 



di Belly white; ears black S. aherti. 



do Belly dark; ears reddish S. kaibabensis. 



