SCIUELD^E. 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. 



SCIUBOPTEKUS, 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. . Scrunus, 2. 

 f f 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. 

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

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

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



/. SCIUROPTERUS, P. Cuvier. FLYING SQUIRRELS. 

 < Pteromys, Cuvier. 



1. S. volans (L.) Coues. COMMON FLYING SQUIRREL. 

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

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



2. SCIURUS, Linnaeus. SQUIRRELS. 



1. S. 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 



