LEFOPJDiE— ANALYSES OF SPECIES AND FAMILIES. 283 



Analysis of the species and varieties. 



I. Skull much arched above ; breadth one half the length ; postorbital pro- 

 cesses distinct, not soldered with the skull ; nasals of medium 

 length, their length equal to about four-fifths of the width of the 

 skull. 



A. Hind feet longer than the head. Size large. Postorbital processes 

 divergent, not in contact with the skull posteriorly. Pelage 

 white in winter. 



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. articus. 



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 surfaces. 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. Washinstoni. 



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

 little or no rufous in summer, and in winter nearly or wholly 

 pure white to the base, the middle reddish band being com- 

 monly almost obsolete var. Bairdii. 



