GEOMYID^B. XII. 29 



FAMILY XI. CASTORID^E. 



( The Beavers.) 



Aquatic Rodents of large size, having the molars 

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

 claws; tibia and fibula distinct; no postorbital process. 

 A small family, containing but two existing genera, 

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



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



CASTOR, 1. 

 /. CASTOR, Linnaeus. BEAVERS. 



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

 now being rapidly exterminated. (C. canadensis, Kuhl.) 



FAMILY XII. GEOMYHLE. 



{The Pouched Gophers.) 



Cheek pouches large and distinct, opening outside of 

 the mouth. Molars f: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 North 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 XIII. ZAPODIDJE. 



(The Jumping Mice.) 



Hind legs greatly elongated, adapted for taking long 

 leaps; fore legs short. Tail very long. Molars f;f; 



