330 Zoological Collection*. 



the anterior surface, not approximate, slightly divergent at their extremi- 

 ty, somewhat analogous to the incisors of the squirrel ; the crowns of the 

 molars are plain, though they do not appear to have been much worn, and 

 are traversed by three, sometimes four folds of enamel, which, in several 

 of the teeth, have no connection with the enamel which encircles them ; 

 in others they consist of re-entering folds, as in the teeth of the beaver ; 

 thus displaying, in a remarkable manner, the extent to which this portion 

 of the structure of the teeth may differ in the same individual : in those 

 instances, where the transverse plates of enamel are distinct from the en- 

 circling enamel, there are no grooves on the side of the tooth ; in other 

 instances, the sides are grooved, as in the teeth of the beaver, except that 

 portion buried in the socket, which is smooth in most instances. In all 

 other details, this skull bears the closest analogy to that of the beaver. 

 The animal was full grown, as is evinced by the teeth, and other particu- 

 lars. 



Habit and Locality. — Nothing further is known concerning the his- 

 tory of this animal, than that its skull was found more than thirty years 

 ago on the shore of the river Delaware, and presented to the Philadelphia 

 Museum ; when first discovered, it was nearly perfect ; by rough usage it 

 has since lost the upper incisors, and part of their alveoles. This cranium 

 has been frequently examined by the curious, and by them regarded as a 

 lusus natures ; the characters which it presents are certainly unique of 

 their kind ; the bony cavities communicating with the mouth, which must 

 Tiave served as receptacles for provision, &c. distinguish this skull from 

 that of all other animals, and particularly the beavers, to which, in other 

 respects, it bears so near a resemblance. That it is not a monstrous pro- 

 duction of nature, is fully demonstrated by the well-defined characters of 

 the jaws and teeth, as well as by the harmonious adaptation of its various 

 parts. It is further, not in the least degree fossilized, nor does it appear 

 to have been totally buried in the ground, inasmuch as one side of the jaw 

 has been bleached by exposure to the sun. 



The first question which presents itself for solution is, from whence came 

 the animal ? are we to consider it as the type of a genus which has become 

 extinct and yet not fossil ? or does it owe its present locality to accident, 

 having been brought from some distant and unexplored country, and here- 

 tofore escaped the eye of the naturalist ? 



The present existing genera to which it is most nearly allied, being 

 known to inhabit only Europe and America, would militate against the 

 latter opinion, and induce us to believe, that this animal did inhabit the 

 countries near which its remains were first discovered, its residence, like 

 that of the beaver, being on the banks of rivers. 



The skull being recent, and not in the least decomposed, the animal 

 could not have been long dead when first discovered. It is most probable, 

 that, in the instance before us, we are presented with the remains of the 

 type of a genus, which has become extinct since the settlement of North 

 America; or, if it still exists, has retreated to the most inaccessible and 

 unexplored forests, which is at least very uncertain. It is more than pro- 



