142 RODENTS OF IOWA 



Key to the Families of Simplicidentata. 



1. Body bearing sharp, stiff spines partly concealed by hair 



(6) Erethizontidae 



Body without spines 2 



2. Tail broad, flattened dorso-ventrally (2) Castoridae 



Tail not broad and flattened dorso-ventrally .' 3 



3. Hind legs and feet markedly elongate; tail very long 



(5) Zapodidae 



Hind legs, feet and tail moderate, not greatly elongate 4 



4. Tail thickly haired and more or less bushy. ..... (1) SciuridaB 



Tail naked or closely or sparsely haired, not bushy 5 



5. External cheek pouches present; claws of front feet 



much elongated (4) Geomyidae 



External cheek pouches wanting ; claws of front feet not 

 greatly elongated (3) Muridae 



Family SCIURID. 

 SQUIRRELS, WOODCHUCKS, SPERMOPHILES, ETC. 



Tail cylindrical, bushy, with long hairs, never covered with 

 scales; postorbital processes distinct; molar teeth rooted, tuber- 

 culate ; first upper premolar small, and sometimes wanting ; cheek 

 pouches, when present, opening inside the mouth. 



Key to the Genera of SciuridaB. 



1. Front and hind legs joined together by a lateral ex- 

 pansion of skin from sides of body. Glaucomys 



Front and hind limbs not joined together by a lateral ex- 

 pansion of skin from sides of body 2 



2.. Length of body from nose to root of tail over 14.00 



inches Marmota 



Length of body" without tail less than 14.00 inches 3 



3. Tail long and bushy; cheek pouches absent or opening 



inside the mouth Scinrus 



Tail moderate or short; cheek pouches present, external 4 



4. Back with two pale stripes and several black ones; no 



rows of pale round spots '. Tamias 



Back with or without stripes; if stripes are present, a 

 series of pale, round spots along the middle of each dark 

 stripe 5 



