SCIURIDJE. X. 27 



distinct. Species of rather small size, widely distributed. 

 The variations in color, etc., are extremely great, and 

 the number of well-defined species is very much less 

 than was once supposed. 



* A densely furred membrane extending along the sides between 

 the anterior and posterior limbs; tail depressed, flattened, 

 densely furred ; permanent molars 5-5 above. 



SCIUROPTERUS, 1. 



** Sides without membrane for " flying." 



f No cheek pouches ; tail bushy, at least as long as body ; ears 

 long; no black stripes along the back. . SCIURUS, 2. 

 ff Cheek pouches present. 



$ Back with 3 to 5 distinct black stripes; tail shorter than 

 body, not bushy; cheek pouches well developed. 



TAMIAS, 3. 



$ Not as above; body rather slender, squirrel-like; cheek 

 pouches well developed; claw of thumb rudimentary 



or wanting SPERMOPHILUS, 4. 



$$ Body large, thick-set, depressed ; cheek pouches shallow ; 

 thumb rudimentary, armed with a small flat nail, not a 

 claw; soles naked. . . . ARCTOMYS, 5. 



/. SCIUROPTERUS, F. Cuvier. FLYING SQUIRRELS. 

 < Pteromys, Cuvier. 



1. S. volucella, (Pall.) Geoff. COMMON FLYING 



SQUIRREL. Yellowish brown, creamy white below. N. 

 Am., abundant. (P. volucella, etc., authors.) 



2. SCIURUS, Linnaeus. SQUIRRELS. 



1. S. niger, Linn. Fox SQUIRREL. Upper molars 

 permanently 4; tail very large and bushy; general color 

 rusty gray, varying from almost white, through various 

 shades of rusty red to jet black, the latter color rare 

 northward, reddish and orange shades predominating 

 westward; L. 26; T. 14. E. U. S., very abundant in the 



