168 — Cineinnats Society of Natural History. 
The entire length of the hind foot was 124% to 12% inches. 
No fragment of either fore foot was preserved. 
III ZOOLOGICAL RELATIONS AND PROBABLE HABITS. 
As is already well known, the zoological relations of this species 
have heretofore been determined almost entirely from the head, 
which Col. Foster thought sufficiently similar to that of Castor to 
warrant the generic name Castoroides, which name later authorities 
have not seen fit to change. 
From important structural differences in the teeth, especially in 
the molars, the relatively small brain cavity, the extraordinary 
modification of the posterior nares, and from other marked differ- 
ences, Prof. J. A. Allen has given it a separate family standing 
under the title Castorotdide. A study of the osteological features 
so far as now developed, will probably warrant this new family 
name, considering the importance of some of the structural rela- 
tions on which it is based. As to the double posterior nares, there 
is a perceptible approximation to the same in the direction and 
position of the internal pterygoid plates of Avctomys. 
Had the first find consisted of molar teeth alone, comparative 
anatomists might have said, here is a gigantic North American 
Chinchilla. Had the head never been seen, and its classification 
based on the feet alone, we would simply say, a new species of 
Castor. Hada tibia and a fibula alone been found, all would prob- 
ably agree that it was strikingly similar to /zber. Had all except 
the head been found, there would have been no occasion to look 
outside the family Castortde. 
Prof. Allen remarks in his Monograph: ‘‘ It will be seen that 
Castoroides presents a singular combination of characters.” ‘That 
it is a generalized rodent type is all the more confirmed from a 
comparative study of the nearly entire skeleton. The case of ° 
anchylosis, involving the axis and the third cervical, is probably 
exceptional. From the very powerful incisors and their massive 
setting, staunchly buttressed as they are on the lingual side, 
together with every evidence of extraordinary muscular strength 
for operating the lower mandibles, does it seem probable that they 
(the incisors) were employed soy for cutting the food needful 
for sustenance ? 
They probably gnawed down trees. ‘The feet afford what 
appears to be satisfactory evidence of having been webbed, indi- 
cating an aquatic life. 
