Family HETEROMYIDAE Pocket Rats and Pocket Mice 



With fur-lined cheek pouches; animals adapted for jump- 

 ing; with long hind legs and tail 

 Four genera — Lwmys 



Perognathus 



Dipodomys 



Microdipodops 

 Family CASTORIDAE Beavers 



Tail broad, flat, scaly; hind feet large and well webbed; claw 

 of second toe split 

 One genus — Castor 



Family CRICETIDAE Native Rats and Mice 



Mouse or rat form; tail scaly hut with hairs; not more than 

 three cheek teeth on each side 

 Subfamily CRICETINAE 



Molar teeth with tubercles in two rows or with enamel 

 folds not forming more than three loops on any tooth 

 Seven genera — Onychomys 



Reithrodontomys 

 Baiomys 

 Peromyscus 

 Oryzomys 

 Sigmodon 

 7\[eotoma 

 Subfamily MICROTINAE 



Molars flat'Crowned, usually with angular infoldings 

 of enamel forming several loops or triangles on each 

 tooth 



Eight genera — Synaptomys 

 Phenacomys 

 Evotomys 

 Microtus 

 Lagurus 

 Pity my s 

 l^leofiher 

 Ondatra 

 Family MURIDAE Old World Rats and Mice 



Mouse or rat form; tail scaly, almost naked; molars with 

 three rows of tubercles 

 Two genera — Mus 

 Rattus 



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