CASTORID 4—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 Kiew Coll), as 
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 asa 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 thatin 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 o/d instead of a young specimen (No. 3672, 
“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 Kuro- 
“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 
g, in the American 
DD) 
skulls, from 0.34 to 0.36 of the length of the skull against 0.38 in two Kuro- 
American average rather shorter than the European, rangin 
