96 CALIFORNIA MAMMALS. 



Family Castoridae. Beavers. 



Skull massive, flat, not constricted interorbitally, nor exces- 

 sively widened posteriorly; zygomatic arches widened posteriorly; 

 no postorbital processes ; nasals short, broad, oval in outer out- 

 line; audital bullae moderately lengthened laterally; descendin,^ 

 ramus of lower jaw wide but of normal shape; molariform teeth 

 single rooted, with the pulp persisting late in life; planes of up- 

 per molars convergent anteriorly; outlets of genito-nrinal and 

 digestive organs combined in one. 



Dental formula, I, i — i ; C, o — o; P, i — i ; M, 3 — 3X2=20. 



The Beavers are a very small family, containing but one 

 living genus, consisting of but two species as now recognized. 

 They are distributed over the colder parts of the northern hemis- 

 phere. The food is strictly vegetable, consisting mostly of twigs 

 and bark obtained by gnawing down trees and shrubs. Their 

 fur is valuable and has been an important article of commerce. 



Beavers are plantigrade, nocturnal, semiaquatic and live in 

 burrows or in "hoiuses" constructed of sticks and mud. The 

 males are somewhat larger than the females but the sexes are 

 otherwise alike and the voung differ but little from the adults. 



Genus Castor Linneus. (Beaver.) 

 Form stout ; tail broad, flat, tongue shaped, covered with 

 scales instead of with hairs; front feet small, not webbed, the 

 inner toe developed but smaller than the others ; no cheek pouches ; 

 pelage consisting of thick fine underfur interspersed with long 

 coarse hairs. 



Castor canadensis frondator Mearns. (Twig-stripper.) 



BROAD-TAILED BEAVER. 



Above russet; below grayish cinnamon; sides wood brown; 

 feet burnt sienna color. 



Length of adult male about 1090 mm. (43 inches) ; tail 



