27 

 MAMMALIA. 



Order Perissodactyla. 



Hoofed quadrupeds, with functional toes in the hind feet, and often like- 

 wise in the fore feet, in uneven number. Arrangement of the constituent 

 lobes of the crowns of the molar teeth unsymmetrical. Femur with a third 

 trochanter. Astragalus with the fore part divided into two very unequal 

 articular facets. 



PAL^EOSYOPS. 



Among the most abundant and interesting of the mammalian remains from 

 the Bridger Tertiary group, which the writer has had the opportunity of 

 examining, are those of a genus of odd-toed pachyderms to which the above 

 name has been given. The specimens consist of fragments of jaws with teeth, 

 isolated teeth, small portions of other parts of the skull, articular ends of 

 the limb-bones, and some of the smaller bones of the feet. 



The anatomical characters of the specimens indicate Palseosyops to have 

 been more nearly related with the tapirs than to any other living animals. 

 The jaws were provided with nearly closed series of teeth in full number, 

 that is to say three incisors, a canine, four premolars, and three molars to each 

 side of both jaws. The canines are as well developed proportionately as in 

 ordinary carnivores, and would lead one to suspect that perhaps Palseosyops 

 used a mixed diet of meat and vegetables. 



The genus was originally established in the Proceedings of the Academy 

 of Natural Sciences of Philadelphia for October, 1870, on specimens of teeth 

 discovered at Church Buttes, Wyoming, during Professor Hayden's geological 

 exploration. It was subsequently indicated in Professor Hayden's Prelimi- 

 nary Report of the United States Geological Survey of Wyoming, published in 

 the spring of 1871, and is there arranged among the artiodactyl or even-toed 

 pachyderms. Much additional material, comprising many parts of the skele- 

 ton of the same genus, having been received from Drs. Carter and Corson, 

 its characters were more fully ascertained, and its true position as a perisso- 

 dactyl or odd-toed pachyderm determined. The later account of these is given 

 in Professor Hayden's Preliminary Report of the United States Geological 

 Survey of Montana, &c, published in the spring of 1872. 



Since then Professor 0. C. Marsh has published a notice in the American 

 Journal of Science of August, 1872, of some remains ascribed to two genera 



