220 Revicivs — Prof. 0. C. Marsh's Dlnocerata. 



diastema. Further back, there are three premolars, and three 

 molars, forming together a close series. This is the dentition, 

 essentially, in the lower jaw of both Dinoceras and Tinoceras. 



" In the genus Tinoceras, the same general characters of the lower 

 jaws are seen. In the male, the pendent process is large and 

 elongate, but less massive than in the genus Dinoceras, and its lower 

 outline less regularly rounded. This corresponds with the position 

 of the larger upper canine tusk, which it protects. In the female of 

 Tinoceras, the pendent process is much reduced, its size in all cases 

 corresponding to the size of the canine tusk above. 



" That the same relation in size between the tusk and process 

 below it holds equally in both the genera Dinoceras and Tinoceras 

 is conclusively shown by various specimens in the Yale Museum. 



" The Teeth. — The teeth of the Dinocerata constitute one of their 

 most interesting features. 



" In the genus Dinoceras, the dentition is represented by the fol- 

 lowing formula : — Incisors %, canines \, premolars f , molars f = 34. 



" So far as now known, the same formula applies equally well to 

 the genus Tinoceras. 



" In Uintatherium, the dentition is apparently as follows : — In- 

 cisors f , canines 1, premolars f, molars f = 36. 



" In none of the Dinocerata have any upper incisors been found, 

 even in the youngest specimens. The premaxillary bones appear 

 to be entirely edentulous. 



" In the lower jaw of all the known Dinocerata, there are three 

 well-developed incisors on each side. They are inserted, each by a 

 single root, and are procumbent, all directed well forward. 



" The superior canines of Dinoceras are long, decurved, trenchant 

 tusks. The crown is covered with enamel, and the root extends 

 upward into the base of the maxillary protuberance, or horn-core. 

 When the animal is young, these tusks grow from a persistent pulp, 

 but in old age the cavity becomes nearly closed. In the male, these 

 tusks are large and powerful, and extend downward nearly or quite 

 to the extremity of the pendent process of the lower jaw. 



" In the female of Dinoceras, the upper canines are small and 

 slender, and protrude but little below the jaw." 



The crowns of the upper premolar and molar teeth in Dinoceras, 

 and, in fact, in all of the known Dinocerata, are remarkably short, 

 with the roots well developed, forming a true brachyodont dentition, 

 as in all early Tertiary ungulates. 



" In each ramus of the lower jaw of Dinoceras, there is a close 

 series of six teeth, three of which are premolars, and three true 

 molars. These are all inserted each by two roots. This is also true 

 of the genus Tinoceras. 



" The molar teeth in Dinocerata appear to resemble more closely 

 the corresponding teeth in the genus Coryphodon than those of any 

 other animal. The general dentition, however, is quite distinct. 

 Coryphodon has well-developed upper incisors, and a medium-sized 

 upper canine, thus differing widely in these features from the Dino- 

 cerata." 



