438 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
ceptible to them was the rather larger size of the American animal. In 
1855, Brandt * made an elaborate study of the subject, arriving at the conclu- 
sion that the New and Old World Beavers were specifically distinct, from his 
finding a few slight but tolerably constant cranial differences, coupled with 
certain differences in the structure of the castoreum-sacs, and in the prop- 
erties of the castoreum itself. Baird,t in 1858, supported the same view, 
without adducing, however, any additional evidence, although inclining to the 
opinion that the American animal was the larger. In 1868, Morgan and Ely ft 
re-examined the subject, having at command a large amount of material, and 
came to the conclusion that, at best, the two animals could be regarded as 
ouly varieties of the same species. 
The evident thoroughness with which Brandt investigated the subject 
has generally led to the adoption of his conclusions, and, consequently, for 
the last twenty years, -the Beavers of the Old and the New World have quite 
currently passed as distinct though closely related species. 
In order to present the subject fairly, I transcribe Brandt’s general sum- 
mary in full, in the words of Dr. Ely’s translation, together with Dr. Ely’s 
valuable comments. Brandt’s material consisted of eight European and five 
American skulls, while Dr. Ely’s series of American skulls exceeded one 
hundred, but embraced only a single European one. By the aid of Brandt’s 
excellent monograph, however, he was able to quite satisfactorily compare 
the two forms. As Dr. Brandt’s paper gives a most elaborate and detailed 
account of the differences observed by him between the crania of the two 
forms, I quote it somewhat at length, using Dr. Ely’s translation in preference 
to the original, since it thereby becomes more easily available to the majority 
of American readers. I also append a summary of Dr. Ely’s comments, 
based, as they are, upon the careful investigation of an exceptionally large 
number of specimens. I furthermore incorporate therewith the results of 
my own study of an additional series of upward of sixty American skulls 
and two European ones. 
Dr. Brandt finds, through his own studies and those of his predecessors 
in the same field, that outwardly there are no satisfactory indications of spe- 
cific difference, either in size, color, the form of the head, ear, or foot, or in 
the scales of the tail; but that the skull affords a number of pretty constant 
*Mém. Acad. St. Pétersb., 6th ser., Sci. Nat., vol. vii, pp. 43-66. 
t Mam. N. Amer., p. 358. 
t The Beaver and his Works, chap. i, and appendix A. 
