SCIURID^. — 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 deusel}'' 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. 



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



body, not bushy; cheek pouches well developed. 



Tamias, 3. 



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



pouches well developed; claw of thumb rudimentary 

 or wanting. .... Spermophilus, 4. 



Xtt Body large, tliick-set, depressed; cheek pouches shallow; 

 thumb rudimentary, armed with a small fiat 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 



