4138 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.f 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 J 

 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 

 only 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 



*M6ru. Acad. St. Pe'tersb., 6th ser., Sci. Nat., vol. vii, pp. 43-66. 



t Mam. N. Amer., p. 358. 



t The Beftvcr and his Works, chap, i, and appendix A. 



