Mustek frenata xanthogenys Gray California Long'tailed 

 Weasel 

 Not so; usually turning white in winter 87. 



87. In summer pelage, color of upper parts extending well on to sides of belly; 

 northern Pacific states 



Mustela frenata washmgtoni (Merriam) Washington Long' 

 tailed Weasel 

 In summer pelage, color of upper parts ending sharply on the sides; Pacific 

 and mountain states 



Mustela frenata nevadensis Hall Mountain Long-tailed Weasel 

 (Includes M. arizonensis (Mearns (part) ) 



KEY TO THE PRINCIPAL GENERA AND SPECIES OF 

 GNAWING MAMMALS 



1. With two very small incisor teeth behind the pair of large upper incisors; 



rabbits or rabbit-hke animals 2. 



With only two upper incisor teeth; not rabbit-like 16. 



2. No visible tail; hind legs not much longer than fore legs; Family 



Ochotonidae Pikas 3. 



With a short tail; hind legs considerably longer than fore legs; Family 



Leporidae Hares and Rabbits 4. 



5. Under parts without bulfy tinge; with an indistinct grayish "'collar" on 

 the shoulders; Rocky and Cascade Mts. southward through Oregon 



Ochotona princeps (Richardson) Rocky Mountain Pika or 

 Cony 

 Under parts with buffy tinge; no grayish collar; in the Sierra Nevadas 

 and mountains between them and the Rockies 



Ochotona schist-iceps (Merriam) California Pika or Cony 

 (Considered to be a subspecies of the preceding) 



4. Hind foot over four and three-quarters inches long in the adult; ears 



often black tipped or black bordered; fur becoming white in winter, 

 in some but not all species, excepting the ears, which are then gray 

 tipped 5. 



Hind foot less than four and one-half inches long; ears usually not so 

 definitely black tipped, but often with a blackish tinge toward the tips; 

 not becoming white in winter Cottontails 9. 



5. Ears and hind legs considerably longer, proportionally, than those of the 



domestic rabbit; ears over three and one-half inches long in the adult 



Jack Rabbits 6. 



Ears not proportionally longer than those of the domestic rabbit; ears 



less than three and one-half inches long Snowshoe Rabbits 8. 



6. No black on tail; fur becoming white in winter in colder parts of its 



range ; from Iowa westward 



Lepus townsendii Bachman White-tailed Jack Rabbit 

 {Lepus campestr-is (Bachman) ) 

 Upper part of tail partly or mostly black; fur not becoming white in 

 winter 7. 



502 



