/ : : 2 3 : P bua 
170 BULLETIN NO. VII. 
most rapidly, leaving little but retrenchment for the following 
periods. 
Eucastor was a genus of small beavers the known examples 
of which were less than half the size of our species. There is 
some reason to doubt if it is more than sub-generically distinct 
from the modern form. 
Steneofiber and Palewocastor are vicarious genera, the one in 
Europe the other in America, which may easily be identical. 
Trogonotherium contained species considerably larger than ex- 
isting beavers. 
GENUS CASTOR. 
Feet five-toed, hind feet palmate; body stout, especially be- 
hind; tail laterally expanded, scaly; skull somewhat as in 
squirrels but without postorbital frontal processes. Molars 
+t, single rooted, the dentinal pulp persisting until a late per- 
iod, triturating surface composed of enamel folds; lower jaw 
massive, symphysis firmly closed. The genus is represented 
at present by a single circumpolar species which may be 
divided into two sub-species or varieties with very close rela- 
‘tions. 
The very careful review of the evidence bearing on the ques- 
tion of the relation of the two forms given in Dr. Ely’s account 
contained in Morgan’s ‘‘Beaver and His Works”, makes a dis- 
cussion of the matter unnecessary. Certain constant but min- 
ute differences in osteology and the nature of the secretion are 
demonstrated, while the importance to be admitted for them 
must be a matter of opinion. 
Castor fiber Linn. 
BEAVER. 
Body thick and heavy, with the greatest diameter near the 
hips, length about 80 inches; tail, 10 inches; the head is broad, 
depressed; nostrils lateral in a naked muffle; ears nearly hidden 
in the fur, rounded; the fore feet are small and are not used in 
swimming; hind feet broad, webbed, second toe often with a 
double claw; color, reddish-brown, darker in winter. The long 
hairs are coarse and glossy, the under pelage soft, fluffy and of 
a grayish color. Melanism is common sorthward, albinoes not 
being rare. The beaver is the largest North American rodent; 
indeed, with the single exception of the capybara, it is the 
Y ~ 4 i % fea 
od ‘ aca ‘ ¥ ern 
