APPENDIX. 



Art. XYIU.— Principal Characters of the Dinocerata ; by 

 O. a Marsh. With five plates. 



The huge Eocene mammals, discovered by the writer in 

 1870, and subsequently placed in the new order Dinocerata, 

 prove to be a well marked group of much interest. The Yale 

 College Museum now contains remains of more than a hundred 

 individuals, some of them in such excellent preservation that 

 few points in the osseous structure of these animals need longer 

 remain in doubt. It is proposed, therefore, to give, in the 

 present communication, the more important characters of the 

 members of this order, reserving the detailed description for a 

 separate memoir. Although several distinct genera of Dinocerata 

 are now known, as shown below, the typical characteristics of 

 the group are best seen in Dinoceras, and hence I describe first 

 that genus, which is especially illustrated in the accompanying 

 plates. 



DijfocEBAs Marsh, 1872.* 



The skull in Dinoceras is long and narrow, the facial portion 

 being greatly produced. The basal line, extending from the 

 lower margin of the foramen magnum along the palate to the 

 end of the premaxillaries, is nearly straight. The top of the 

 skull supports three separate transverse pairs of osseous eleva- 

 tions, or horn-cores, which form its most conspicuous feature, 

 and suggested the name of the genus. The smallest of these 

 protuberances are situated near the extremity of the nasals ; a 

 second much larger pair rise from the maxillaries in front of 

 the orbits ; while the largest are on the parietals, and supported 

 by an enormous crest, which extends from near the orbits 

 entirely around the lateral and posterior margins of the true 

 cranium. (Plate II.) The posterior crest, which curves up- 

 ward and backward beyond the occipital condyles, is mainly 

 composed of the supra-occipital. The floor of the deep depres- 

 sion in front of this crest is formed by the parietals. These 

 bones also send up the lateral crests. The top of the skull 

 between the orbits is formed of the frontal bones, which are 

 remarkably short. Their superior sutures with the parietals 

 pass just in front of the lateral crest, and then converge poste- 

 riorly. There is no postorbital process, but in some species of 



* This Journal, iv, 343, v, 117, 293 and 310. 



