54 The Extinct Rodentia of North America. (January, d 
number ot species in both the eastern and western continents, 
of inferior size and more restricted distribution. The greater 
number of these belong, I believe, to the same genus as 
the Castor fiber, though 
they have been separated 
under the name of Steneo- 
fiber Geoffr. There is no 
essential difference in the 
dentition, and it is probable 
that. the extinct species had 
the peculiar flat tail of the 
dal vertebrz of the C. pan- 
sus, from Nebraska, have 
exactly the character of 
those of the beaver. 
The family of the Castor- 
ide differs from the Sciuri- 
dz in the absence of post- 
orbital angles or processes, 
and the presence of a pro- 
auditorius externus. In 
both ofthese points it agrees 
with the Haplodontiide, a 
distinguished from the Cas- 
toridæ on various grounds. 
I do not think any of his 
characters are tenable, ex- 
cepting that drawn from 
the form of the mandible, 
which is expressed thus in 
Fic. 10.—Skull and bones of cane pore ed ul i f mandi- 
sulatus Cope, represented in S P S . 
Fig. 9. occi- : 
pital view; 4, c, right ramus of pact Bet d, ble much twisted.” This — 
right femur. Natural size. character will be better de- 
scribed as follows: Angle of mandible with a transverse edge 4 
due to inflection on the one hand, and production into an ie ; 1 
externally; the inflection bounding a large interno-posterior fossa. 
modern beaver. The cau: 
family which Mr. Alston has ~ 
Mr. Alston’s diagnosis: 
longed tube of the meatus j 
2i 3 E E E E EEA à 
EF SE E E ey O ES E R EAEE a E ATA E E 
E aa 
i oe aa 
