APPENDIX. 



Art. XLI. — Principal Characters of the BRONTOTHERIDiE ; 

 by O. C. Marsh. With four plates. 



The 



! mammals 



LHE remams oi a weli-marked group or gigan 

 abundant in the lowest deposits of the Mio 

 eastern slope of the Kooky Mountains. These animals, which 

 have been named by the writer, Brontotheridce, equaled the 

 Eocene Dinocerata in size, and resembled them in some im- 

 portant features. They do not, however, belong to the same 

 order, but constitute a distinct family of Perissodactyles. Four 

 genera of this family are now known, as shown below, but 

 Brontotherium is the only one represented by sufficient remains 

 to clearly indicate its structure and affinities ; and hence this 

 genus will be first described, and mainly used to illustrate the 

 group. 



Brontotherium Marsh, 1873.* 

 The skull in Brontotherium is long and depressed, and re- 

 sembles that of Rhinoceros. The occipital region is extended 

 vertically, and deeply concave posteriorly. The vertex is con- 

 cave longitudinally, and convex transversely. The general 

 form of the skull is shown in the cut given below, figure 1. 



^., 



There is a pair of large horn-cores on the i 

 skull, m front of the orbits. They stand 



2.s^!ii^'^,^ VOL y, p. 486. A 



