RODENTIA. CASTORID^. 51 



Castor fiber. Lin. The Beaver. 



Castor Fiber, Harlan, p. 122. 

 The Beaver, Godman, Nat. Hisr., ii. p. 21. 

 Castor Fiber American us, Richardson, p. 105. 

 Figure ; Godman, ii. p. 21. 



Specific characters. The fur consists of two sorts of hair, one 

 coarse and brownish, the other downy, more or less gray. 



Description. The head of the Beaver is rather large, with a 

 short and blunt snout ; the upper lip is divided ; eyes and ears 

 small ; body thick ; the fore limbs somewhat stouter than the 

 posterior ; feet five-toed, the membrane forming the web broader 

 on the posterior than on the anterior feet ; middle toe longest, all 

 armed with strong nails, fit for burrowing ; tail flattened trans- 

 versely, oval, broad, and covered at base with thick fur, the re- 

 mainder covered with scales. Incisors yellow in front, strong, 

 and furnished with a single plate of enamel ; the upper stand at 

 right angles to the axis of the jaw ; molar teeth of the upper jaw 

 directed backwards and outwards ; each tooth upon the inside 

 presents a distinct longitudinal groove, formed by the folding of 

 the enamel upon itsalf, and which divides it into two nearly equal 

 parts ; on the outside, the two middle teeth present two indistinct 

 grooves, and the extremes are merely striated ; the lower molars 

 are directed forward and inwards ; the outside presents a strong 

 groove dividing it into two parts by the folding of the enamel, 

 while, upon the inside, there are three rather distinct grooves 

 formed in the same manner by the enamel, but less distinct than 

 the single outside groove. When the tooth is worn down, the 

 enamel upon the inside presents three foldings upon itself, but on 

 the outside, only one ; the middle folding is the shortest, and the 

 point of flexure is a little in advance of the one from the outside, 

 in the first tooth, which is always less worn than the others, in 

 which the middle foldings stand face to face. In the upper molars 

 the inside groove throws the smallest division of the tooth to the 

 anterior side, and the posterior half has one general fold of enam- 

 el, which embraces two foldings from the outside, an arrangement 

 the reverse of that in the molars of the lower jaw ; the inferior 



