Castoroides Ohioensis. 401 
inches, and its greatest breadth 7.9 inches. According to 
Professor Emmons, the skull of an old female beaver, meas- 
ured, from the tip of the nose to the crucial ridge, 4.9 inches, 
and its greatest width 3.9 inches ;' an adult skull in my own 
cabinet gives precisely the same measurements. The skull of 
the Castoroides is therefore a little more than double the size 
of that of the common beaver, (Castor fiber.) According to 
Dr. Richardson, the largest. beavers which he had an oppor- 
tunity of measuring, had a length of 2 feet, 6 inches; Dr. 
Godman estimates the average length at about 2 feet; assum- 
ing the proportions of the Castors and Castoroides to be the 
same, we should have the entire length of the latter amount- 
ing to about 5 feet. 
The generic characters of the Castoroides which have been 
deduced from the cranium just described, and which, on com- 
Parison, will be found to differ materially from those given by 
r. Foster, are as follows.? 
Teeru. Incisors, 1 1; Canines, ??; Molars, 2 1; total, 20. 
Molars consist of thin lamine of dentine, surrounded by 
enamel, and united by crusta petrosa. The first in the up- 
Per and the last in the lower jaw, have four such laminz, 
and the remaining teeth have only three each ; the grinding 
surface is slightly concave in the lower jaw, and slightly con- 
vex in the upper, the enamel forming only a very small pro- 
lection above the dentine and crusta petrosa. The internal 
pterygoid fossze are largely developed, and the internal ptery- 
goid processes are so far deflected inwards as to touch on the 
median line, and divide the entrance to the posterior nares - 
transversely, thus forming a superior and an inferior orifice. 
, Report on the Quadrupeds of Massachusetts, p. 51. 
: * Common usage scii iois would justify us in substituting a new — 
oF that of Castoroides, especially since the generic characters have been very differ- 
ently defined from what they were in the orìginal description. The name Castor- 
ides, however, having gone into general use, it would therefore seem desirable that 
?! should be retained, i 
