MAMMALS 327 



except in the Australian region; about 9 genera and 90 species in the 

 United States and Canada. 



Key to These Subfamilies 



ai No flying membrane present i. Sciurince. 



ao Flying membrane present; flying squirrels 2. Pteroviyince. 



Subfamily i. Sciurinae. — Squirrels; chipmunks; ground squirrels; 

 prairie dogs; woodchucks: 9 genera. 



Key to These Genera 



ai Tail long; body slender. 



bi Cheek-pouches absent; tail very long i. Sciurus. 



b-: Cheek-pouches present; tail moderate. 



Ci Thumb with well developed nail; chipmunks. 



di Premolars i/i ; eastern chipmunks 2. Tamias. 



do Premolars 2/1; western chipmunks (Fig. 181). .3. Eutamias. 

 C2 Thumb with rudimentary nail (Fig. 182); ground 

 squirrels, 

 di Back and sides broadly striped. 



Ci Tail not curved over the back 4. Callosperniophiliis. 



6-2 Tail curved over the back 5. Animospermophilus. 



di Back and sides not broadly striped, either finely 

 striped or spotted or uniform in color. 



ei Size large; length over 500 mm 6. Otospermophilus. 



eo Size small; length under 300 mm 7. Citellus. 



a2 Tail short; body stout and heavy. 



bi Length 400 mm. or less; prairie dogs 8. Cynomys. 



b; Length over 600 mm.; woodchucks 9. Manrwta. 



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

 hairs being longest on the sides; ears and eyes large; thumb rudimen- 

 tary; dentition i/i, 0/0, 2/1, 3/3: over 100 species; cosmopolitan, 

 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; 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 5. hudsonicus. 



