GEOMYiD^. — xn. 29 



FAMILY XI. — CASTORID^. 



( The Beavers.) 

 Aquatic Rodents of large size, having the molars 

 rootless, f:|, or f:f ; fore feet with five distinct toes and 

 claws; tibia and fibula distinct; no postorbital process. 

 A small family, containing but two existing genera, 

 Haplodontia of our N.W. coast, and Castor. 



* Molars 4-4 above ; hind feet webbed ; tail broad, flat, and scaly. 



Castor, 1. 

 /. CASTOR, Linnieus. Beavers. 



1. C. fiber, L. Beaver. Mexico to the Polar Sea; 

 now being rapidly exterminated. ((?. ctmadensis^ Kuhl.) 



FAMILY XII. — GEOMYIU^. 



{The Pouched Gophers.) 

 Cheek pouches large and distinct, opening outside of 

 the mouth. Molars J:|; incisors large and thick; skull 

 heavy; temporal bones enormously developed. Limbs 

 about equal, the fore claws, five in number, very large; 

 tibia and fibula united. Body thick-set and clumsy. 



Genera two, Geomys and Thomomys.^ all Nc rth Ameri- 

 can, and chiefly inhabiting the central plains; habits 

 nocturnal and subterranean. 



* A large groove near the middle of each upper incisor ; crown 



of molars elliptical Geomys, 1. 



/. GEOMYS, Rafinesque. Pouched Gophers. 



1. G. bursar/us, (Shaw) Rich. Pocket Gopher. Red- 

 dish brown, with plumbeous tinge. Prairies, Wis. and 

 Ills., westward. 



FAMILY XIIL — ZAPODID^. 



{The Jumpmg Mice.) 

 Hind legs greatly elongated, adapted for taking long 

 leaps; fore legs short. Tail very long. Molars ^:^; 



