'fffi 



:i' ^^! 



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■■ii 



444 



MONUUUAi'UH OF NORTH AMEUIOAN KODKNTIA. 



to invalidate! the roncliisions I lint tlio Kuropenn and the American Urnvor 

 constitute dirtcrent s|ie(!ii'ti. The extremes of diU'ercnee, in their iiggrcf^ute, 

 on the one side mid on the other, nrc sutticiently striking to juotify uh in 

 regarding them nti varieties of one and the same species; while the want uf 

 constancy in these peculiarities suggests the inference, th:it these variations 

 are due to long separation uf the races, and to accidental causes, rather than to 

 original diversity of the stock. It is conceded by the advocates of a diversity 

 of species that the Beavers of the Old and the New World cnnnut be dis- 

 tinguished by any external characteristic. The same is true of their habits 

 and instincts, except so far us they have l)een evidently controlled by external 

 influences. The castoreum secretion is variable, even in the European 

 Ueavers, and there are tiicts to show that the elements of the food of tiie 

 nnimul arc found in it.* The differences observed in il, being more ot degree 

 than of kind, are not of such a character as to render it improbable that they 

 are due to tlie intluence of climate, food, and accidental cau8es.''f 



A careful analysis of the above-noted cranial differences between the 

 European and American Beavers shows that they consist mninly in (1) the 

 greater general breadth of the anterior portion uf the skull, resulting in n 

 greater interorbital breadth, wider nasal bones, wider muzzle, and consequently 

 wider incisors; (2) the relatively greater posterior extension of the nasals; 

 {'A) the greater size and dcptii of the basilar cavity ; and (4) in less marked 

 and rather more inconstant teatnresof diflerence inafew other points. Con- 

 ceding with Dr. Ely their varietal or subspecitic distinctness, the two forms 

 may be thus conveniently diagnosed : 



Castor Jib'' r var. _/?A^;.— Dorsal surface of the interorbital region gener- 

 ally as bruad as, or broader than, long ; nasals extending backward beyond the 

 posterior border ofthe anterior orbital process; basilar cavity deep and large ; 

 bulliE placed more anteriorly, etc. 



Castor Jiber var. canadensis. — Dorsal surface of the interorbital region 

 generally lunger than broad; nasals generally not reaching beyond the middle 

 of the anterior orbital process ; basilar cavity comparatively shallow, etc. 



Synonymy and Nomenclature. — In respect to the distinctive name ofthe 

 American form, that oi canadensis of Kuhl evidently has priority; the amrri- 



' Tku casturvuni of I be Anieriuaii Beaver is weU knowu lo diffiT very iiiBti-riully from thai n( llie 

 Old Wurld Beaver, and ban a very tnncb Hmaller comoierclal value. Chemical analyaes abow that tbe 

 coatureuin of tbo KiiMiau Ucaver cuiitaiaa mora volatile oil, caatorio, aod reain, and much leaj carbonate 

 of lime, than tbat of the American Beaver. 



t Morgaii'H " Tbe Ilcaver und bis Work*", p. StW. 



