370 The Extinct Rodentia of North America. [Apri 
THE EXTINCT RODENTIA OF NORTH AMERICA. 
BY PROFESSOR E. D. COPE. 
( Continued from page 174.) 
PLIOCENE AND POST-PLIOCENE RODENTIA. 
CASTOROIDES Foster. 
The only known species of this genus, the C. ohioensis Fost, 15 
the largest of the order. It is found in the post-glacial deposi 
with the Mastodon ohioticus, in rather limited numbers. 
Mr, J. A. Allen, of Cambridge, has studied the affinities of this 
genus, and states them as follows: “ Castoroides presents asi 
a 
~ - 
eee sie on agi 
E 
roris 
in 
FIG. 22.—Castoroides ohioensis Fost., two-fifths natural size. > m 
attachment of masseter muscle; 4, Deep fossa below sigmoid note ramen 
cy External auditory meatus; g, Superior and inferior incisors; ¢ Fo 
bitale. From Hail and Wyman. . 
oe one ne hand,” | 
gular combination of characters, allying it, on the © Vis 
the beaver, and, on the other, to the chinchillas and É parate 
and also to the muskrat, but which at the same time 5 
widely from either group.” m tho® © 
. > . . o! | 
“ The molars differ strikingly in structure not only p che | 
of Castor, but from those of all other rodents except Ad 
