72 



The singular character of the animal was first recognized in a fossil specimen, 

 consisting of a mutilated lower jaw, discovered by Dr. Carter in the vicinity 

 of Fort Bridger, and sent to the writer in the spring of 1871. The specimen, 

 represented in Figs. 1 to 3, Plate V, besides the two large incisors, contains the 

 remains of most of the molar teeth, but none in an entire condition. The 

 best preserved is the second molar of the left, side, and this is so much worn 

 as to have the distinctive features of its triturating surface, as seen in Fig. 2, 

 completely obliterated. 



The specimen was originally described in the proceedings of the Academy 

 of Natural Sciences in May, lb71, and from its peculiarities the animal to 

 which it belonged was named Trogosus castoridens, or the beaver-toothed 

 gnawing hog. Professor Marsh had previously described, an isolated tooth, 

 of the same animal, from Grizzly Buttes, which he referred to a species of 

 Palasosyops with the name of P. minor. From the description, I supposed it 

 not to differ from P. pedudosus. An examination of the specimen has satis- 

 fied me that it belonged, to the same animal as the jaw referred to Trogosus. 



The isolated tooth belonged, to a younger animal, and is not so worn as to 

 have the characteristic arrangement of its masticating surface destroyed. On 

 seeing it I was struck with its resemblance to another isolated molar tooth 

 which I had formerly described under the name Anchippodus riparius. This 

 tooth was discovered by Dr. Knieskern in a Tertiary formation, supposed to 

 be of Eocene age, in Monmouth County, New Jersey. It was given to Mr. 

 T. Conrad, by whom it was presented to the Academy of Natural Sciences 

 of Philadelphia. The same formation has yielded the remains of a peccary, 

 an Elotherium, and a. rhinoceros. 



A comparison of the tooth of the New Jersey Anchippodus with the cor- 

 responding one in the jaw-specimen and with the isolated molar, would appear 

 to indicate that the Wyoming fossils belong to the same genus, and indeed 

 the teeth are sufficiently alike in form and size to pertain to the same species. 

 Should further discovery prove this to be the case, it would, perhaps, indi- 

 cate the contemporaneous character of the Bridger Tertiary formation of 

 Wyoming and that of Monmouth County, New Jersey. The New Jersey 

 fossil, in its general appearance of color and condition, so closely resembles 

 the Wyoming fossils that it would readily pass for one of them. 



It is by no means positive that Trogosus and Anchippodus are the same, 



