1875.] 431 [Allen. 



a. Size large. Nasals about as wide in front as behind. 



1. Ears rather shorter than the head. Pelage dusky yellowish 



gray in summer, pure white to the roots in winter. Tail 

 short, black above in summer. Size very large. 



timidus var. arcticus. 



2. Ears much longer than the head. Pelage pale yellowish 



gray in summer, in winter white at the surface and base, 

 and reddish in the middle. Tail long, white on both sur- 

 faces. Size smaller campestris. 



b. Size medium. Nasals considerably narrower in front than 



behind. 



3. Ears about equal to the length of the head . . americanus. 



3a. Pelage in summer pale cinnamon brown ; in winter 

 white at the surface and plumbeous at base, with 

 a narrow middle band of reddish brown. 



var. americanus. 

 3b. Pelage in summer cinnamon brown; in winter white 

 at the surface and plumbeous at base, with a 

 broad middle band of reddish brown, which shows 

 through the white of the surface, the white being 

 often a mere surface wash. Fully as large, or 

 rather larger than var. americanus. 



var. virginianus. 

 3c. Pelage redder in summer and whiter in winter than 

 in the last, and size smaller. 



var. Wasldngtoni. 



3d. Size of the last, with the pelage more dusky in 



summer, and in winter nearly or wholly pure white 



to the base, the middle reddish band being more or 



less obsolete var. Bairdii. 



B. Hind feet not longer than the head. Size small. Postorbital 

 processes convergent, frequently (in old specimens) in con- 

 tact with the skull posteriorly, but only rarely anchylosed 

 with it. Pelage never white. 



4. Gray above, varied with black, and more or less tinged with 



light yellowish brown ; under parts white . . sylvaticus. 

 4a. Above yellowish brown, with a tinge of reddish. 



var. sylvaticus. 



