50 Prof. E. D. Cope — A New Perissodactyle Ungulate. 



words, the leading facts in reference to this remarkable Eocene 

 Mammal. 



" A New Type op Perissodactyle Ungulate. 



In a paper on the ' Homologies and Origin of the Molar Teeth of 

 the Mammalia Educabilia,' published in March, 1874, I ventured 

 the generalization that the primitive types of the Ungulata would be 

 discovered to be characterized by the possession of five-toed planti- 

 grade feet, and tubercular teeth. No Perissodactyle or Artiodactyle 

 mammal was known at that time to possess such feet, nor was any 

 Perissodactyle known to possess tubercular teeth. Shortly after 

 advancing the above hypothesis, I discovered the foot structure of 

 Coryphodon, which is five-toed and plantigrade, but the teeth are 

 not of the tubercular type. For this and allied genera, I defined 

 a new order, the Amblypoda, and I have published the confident 

 anticipation that genera would be discovered which should possess 

 tubercular (bunodont) teeth. This prediction has not yet been 

 realized. I now, however, record a discovery, which goes far to- 

 wards satisfying the generalization first mentioned, and indicates 

 that the realization of the prophecy respecting the Amblypoda is 

 only a question of time. 



In 1873 I described, from teeth alone, a genus under the name of 

 Phenacodus, and although a good many specimens of the dentition 

 have come into my possession since that date, I have never been 

 able to assign the genus its true position in the mammalian class. 

 The teeth resemble those of suilline Ungulates, but I have never had 

 sufficient evidence to permit its reference to that group. Allied 

 genera recently discovered by me have been stated to have a hog- 

 like dentition, but that their position could not be determined until 

 the structure of the feet shall have been ascertained. 



In his recent explorations in the Wasatch Eocene of Wyoming, 

 Mr. J. L. Wortman was fortunate enough to discover a nearly entire 

 skeleton of a Phenacodus very near the typical P. primcevus, which 

 presents all the characters essential to a full determination of its 

 place in the system. The unexpected result is, that this genus must 

 be referred to the order Perissodactyla and the Proboscidea, and 

 that, with its allies, it must form a special division of that order 

 corresponding in the tubercular characters of its teeth with the 

 bunodont or suilline division of the Artiodactyla. In this character, 

 however, there is a closer gradation than in the case of the 

 Artiodactyla, and it would scarcely be necessary to create such a 

 group on that character alone. But the genus differs further from 

 the Perissodactyla and approaches the Proboscidea, in the fact that 

 the astragalus articulates with the navicular only, and by a 

 universally convex surface, as in the Carnivora. 



The astragalus resembles that of the latter order very closely, and 

 differs from that of Hyracotherium and the nearest forms among the 

 Perissodactyla. Phenacodus has, moreover, five well-developed toes 

 on all the feet, and was probably not entirely plantigrade. The cast 

 of the brain-case shows that the cerebral hemispheres were quite 

 small and nearly smooth, and that the very large cerebellum and 



