CASTORID^E -CASTOR— CASTOR FIBER. 441 



anterior half of the nasal bones is in six of the European skulls pretty plane; 

 in two of the others, on the contrary (Nos. 51 and 1955 of the Kiev.- Coll), a*5 

 in all the five American, it is strongly convex. In regard to the character 

 (or relation) of the nasal bones, there remains, therefore, in consequence of the 

 preceding remarks, only their more considerable length in comparison with the 

 skull as a mark of the European Beaver; since the greater lengthening poste- 

 riorly of the nasal bones cannot be so rigorously proven in all European Beavers, 

 especially not in our Lapland specimens. It is possible, however, that the' 

 nasal bones are less prolonged posteriorly in younger animals than in full- 

 grown, so that in this way the full-grown European might be recognized by 

 its posteriorly prolonged nasal bones. Confirmatory of this view are the fol- 

 lowing facts : 1. That in all of the six old skulls lying before me of European 

 Beavers, the posterior extremities of the nasal bones reach more or less far 

 posteriorly, and that this happens in a young skull of the Kiew Collection 

 (No. 57), the length of which is four lines greater than that of the one from 

 Lapland; and, 2, that in one very young American skull, the nasal bones 

 extend backward somewhat less relatively than in the full-grown." 



As Dr. Ely remarks, it is in respect to the nasal bones that the greatest 

 difference has been observed between the European and American Beavers. 

 This difference was long since pointed out by both the Cuviers, and later con- 

 firmed by Owen as well as Brandt. The greater posterior prolongation is 

 not, however, constant, as shown by Brandt himself, and in one of the Euro- 

 pean skulls now before me, a very old instead of a young specimen (No. 3b72, 

 " Skagit River "), they do not extend beyond the point reached, by one-fifth 

 of the American skulls now before me. In none of the American skulls, 

 however, do they attain the posterior extension ordinarily seen in the Euro- 

 pean. In sixty American skulls, the nasals terminate posteriorly, in one-fifth 

 of them, about opposite the middle of the anterior orbital process; in nearly 

 one-half, they terminate opposite the hinder margin of the anterior orbital 

 process ; in eight others, they advance a little more posteriorly ; and, in twelve 

 others, pass slightly beyond this point, exactly corresponding in this respect 

 with frequent specimens of the European Beaver. In one American speci- 

 men, the nasals do not quite reach the point opposite this process. In respect 

 to their relative length, as compared with the whole length of the skull, the 

 American average rather shorter than the European, ranging, in the American 

 r.kulls, from 0.34 to 0.36 of the length of the skull against 0.38 in two Euro- 



