GO 

 HtKACHYUS AORAEIU8. 



TJiis species, originally indicated and named from the specimen repre- 

 sented in Fig. 11, Plate II, consisting of a ramus of the lower jaw without 

 teeth, we have now the opportunity of illustrating by many well-preserved 

 and more characteristic specimens. Most of these were collected by Dr. J. 

 Van A. Carter, during the last summer, on Henry's Fork of Green River, 

 near Lodge-Pole Trail, at Bridger Butte, and other localities in the vicinity of 

 Fort Bridger, Wyoming. A few others were obtained by Dr. Joseph K. 

 Corson, from Grizzly Buttes, Wyoming. 



The specimen represented in Fig. 12, Plate II, being one of those upon 

 which the genus Hyrachyus was originally proposed, was referred to another 

 species from the former one, with the name of Hyrachyus agrestis. This I now 

 regard as of the same species. The specimen, a lower-jaw fragment, belonged 

 to a young animal, which still retained its temporary teeth. Of these, the 

 fossil contains the first premolar, the fangs of the succeeding two, and the 

 molar tooth. Behind this the first molar of the permanent series is inclosed 

 within the jaw. 



Professor Marsh has described remains apparently of the same animal 

 under the name of Lophiodon Bairdianus. The specimens, which he observes 

 are among the most common of the mammalian fossils of the Wyoming Ter- 

 tiary, were found at various localities near Fort Bridger, and also on the 

 White River, in Eastern Utah. 



The dental series of Hyrachyus agrarkcs, in the mature condition, consists 

 of three incisors, a canine, four premolars, and three molars, in both jaws. 



A well-preserved series of upper molar teeth, considerably worn, is repre- 

 sented in Figs. 9 and 10, Plate IV, from a specimen discovered by Dr. Car- 

 ter near Lodge-Pole Trail, about eleven miles from Fort Bridger. Fig. 11, 

 of the same plate, represents an upper second molar, which was obtained by 

 Dr. Carter on Henry's Fork of Green River. 



Of the upper molars, or true molars, the middle one is the largest, and the 

 others are nearly equal in size. Four principal lobes enter into the constitu- 

 tion of their crown, which is inclosed by a basal ridge, except externally, and 

 at the most prominent portion of the inner lobes internally. Of the outer 

 lobes, which are conjoined, the posterior is the wider and is pyramidal ; the 

 anterior is the more prominent externally and is conical. This is also strength- 

 ened in front by a large conical buttress continuous with the comparatively 



