CASTOR. 139 
to live in perfect harmony in the same burrow. Full references to the literature of 
this subject will be found in Mr, Allen’s monograph‘. 
Fam. II. CASTORIDA. 
1. CASTOR. 
Castor, Linneus, Syst. Nat. i. p. 78 (1766). 
The remarkable family of Castoride contains only a single genus, which until lately 
has been generally considered to consist of two distinct though closely allied species, 
respectively characteristic of the Palearctic and Nearctic Regions. First systematically 
separated by Kuhl*, the specific distinction of the American Beaver was insisted on by 
the two Cuviers?; and the question was more fully worked out by the late Professor 
J. F. Brandt. The last-named careful zoologist disposed satisfactorily of most of the 
external characters which had been supposed to exist ; but a comparison of eight Euro- 
pean and five American skulls led him to support the specific distinction of Castor 
canadensis, as indicated by several cranial peculiarities, notably by the proportional 
narrowness of the facial region and comparative shortness of the nasal bones. 
In 1867 the question was reconsidered by Dr. W. W. Ely, of Rochester, New York §, 
who was enabled, by the examination of a very large series of American Beaver skulls, to 
show that a great amount of variety existed in the very points on which most trust had 
been reposed. Mr. Allen has since confirmed Dr. Ely’s observations |], which render it 
clear that although the characters of the breadth of the facial region and the length of 
the nasals are generally available, they are by no means constant. The number of 
Beavers’ skulls to which I have access is not sufficient to enable me to add to the facts 
adduced by the American writers; but from the whole evidence it appears clear that the 
Beavers of the New and Old Worlds are not fully differentiated, and must be regarded 
as geographical races of a single circumpolar species. 
1. Castor fiber. 
Castor fiber, Linneeus, Syst. Nat. i. p. 78 (1766, descr. orig.)'; Allen, Mon. N.-Am. Rodent. 
p- 433’. 
Castor canadensis, Kuhl, Beitr. z. Zool. p. 64 (1820, descr. orig.)*; Baird, Mamm. N. Am. p. 355° ; 
Rep. U.S. Mex. Bound. Surv. ii. Mamm. p. 40”. 
* Beitr. z. Zool. p. 64. 
+ Mammif. iii. pl. 274 (51° livr.) ; Ossem. Foss. (3° éd.) v. p. 57. 
+ Mém. Ac. Pétersb. 6° sér. vil. pp. 43-76, pls. i—ili. 
§ Morgan’s ‘ American Beaver and his Works’ (Philadelphia, 1868), Appendix A, pp. 287-306, 
|| Mon. N.-Am. Rodent. pp. 437-445. 
T 2 
