w 



m* 



! 



432 



MONOOKAPII8 OF NOUTU AMKKICAN KODBXTIA. 



kIzc, and \\w. griiieral struct iinj of tlu! skull indicatt^s great incisive power, tlie 

 Beavers iicing '^ gimwGrn" pur excellence. 



Tli(! living reproseiitntives of" the family Ciustoridce belong to the single 

 geiuis Castor. Beaver-like animals, belonging to five or six other genera, 

 hnv(!, however, l)een referred to the sunie group. Some of these {Steneqfiber, 

 including Palaocastor Lcidy and Chalicoinys) differ widely from Castor, while 

 one (Castoroutes) is more nearly related to the Chinchillas (Lagostomus) than 

 to any other family of Rodents. Others ( Trogont/ierium and Eucastor) evi- 

 dently are closely reUxted to Castor. The extinct genera, above named, are 

 us yet known from too scanty materials to render certain their true affinities. 

 Trogontherium, whose remains occur sparingly in the Tertiary deposits of 

 Europe, evidently greatly resembled Castor ; it was, however, fully one-fiflh 

 larger, and in its dentition difTers generically from Castor. The genus Eucas- 

 tor, known as yet from very imperfect cranial remains found in the Mauvaises 

 Terres of Dakota, of the size of a Marmot (Arctomys), seems to have been 

 a true Beaver, apparently as closely related to Trogontherium as to Castor. 

 Chalicoinys and Steneqfiber differ considerably both in dentition, and in the 

 general form of the skull, from the true Beavers, and may prove, when better 

 known, to pertain to an entirely different group. Chalicomys has thus far been 

 found only in the Tertiary formations of Europe, while Steneqfiber had rep- 

 resentatives not only in Europe, but in the Tertiary formations of New 

 Mexico and Dakota. 



The genus Castoroides, heretofore always referred tx) the Castoridte, has, 

 as already shown,* only a superficial resemblance to the true Beavers. 



Genus CASTOR Linn. 



Cmtor Limn., Syst. Nat., i, 1766, 178. 



Chars, — Feet four-toed ; hind feet palmate, with the second toe double- 

 clawed. Tail broad, flat, and scaly. Body stout and heavy, most strongly 

 developed posteriorly. Grinding-teeth Jri-, single-rooted, with the dentinal 

 pulp persisting to a late period of life. General form of the skull as in the 

 Sduridts, but lacking the postorbital processes, and otherwise differing. 



Represented by only a single living species {Castor ^ber), whose habitat 

 formerly embraced the greater part of the northern hemisphere. Remains 

 of Castor have been described from the Tertiary deposits of Europe, which 



* B«e the preceding Monograph. 



