SCIUKLDJG. 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. 



SCIUKOPTERUS, 1. 



** Sides without membrane for &quot; flying.&quot; 



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

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

 ft 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. 

 &amp;lt; PteromyS) Cuvier. 



1. S. vo/ans (L.) Coues. COMMON FLYING SQUIRREL. 

 Yellowish brown, creamy white below. N. Am., abun 

 dant. (P. volucella, etc., authors.) 



2. SCIURUS, Linnseus. SQUIRRELS. 



1. 5. cinereus, 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 



