Cope.] 558 |- Jan> 18i 



those of the lower jaw, I suspect that the former were absolutely wanting 

 in this genus. If so, we have in the Orcodont line the same process of re- 

 duction above, as has taken place in other lines of Artiodactyla at the 

 latest or modern stage of their history. 



In Pithecistes the inferior canine is caniniform, and masticated in con- 

 tact with the superior canine, owing to the great abbreviation of the sym- 

 physeal region. 



The diagnosis of the genus is as follows : 



Inferior premolars three ; incisors one. Canine caniniform, masticating 

 with the superior canine. No diastema. Symphysis coossified. 



Two species are referred to this genus without conclusive evidence as to 

 the number of their premolars. It is probable that they have but three, 

 since their superior fourth premolars are of reduced size and incomplete 

 type of form. 



Pitliecistes forevifacies Cope. 

 Proceedings American Philosophical Society, 1877, p. 219. 

 Ticholeptus beds of Deep river, Montana. Discovered by J. C. Isaac. 



Pithecistes decedens Cope, sp. nov. 



Established on a right maxillary bone, which contains the fourth pre- 

 molar, the first and second true molars, and part of the alveolus of the 

 third true molar. The last named tooth was not probably entirely pro- 

 truded. This, with the moderate wear of the fourth premolar indicates that 

 the animal was fully grown, though young. 



The species differs from all the members of the family whose dentition 

 is known to me in the small size and simplicity of structure of the fourth 

 premolar. The internal crescent of this tooth bounds only the posterior 

 three-fourths of the external wall, and therefore leaves the anterior edge 

 of the latter free. It is, moreover, not very convex, and its edge is not so 

 elevated as is that of the external wall. The latter is flat on the external side, 

 and its anterior marginal angle corresponds with the point of junction of 

 the anterior extremity of the internal crescent. The true molars have the 

 anterior horns of their crescents prominent, being sections of well-de- 

 veloped vertical columns. In this they differ from those of the P. 7ietero- 

 don, where these ridges are very weak. 



The malar process of the maxillary bone is robust and prominent, and 

 begins to expand opposite the first true molar. It presents a tuberosity 

 downwards. The infraorbital foramen issues above the front part of the 

 fourth premolar. 



Measurements. M. 



Diameters P ra. iv / anteroposterior. . . .006 



{ 



transverse 005 



Diameter m. i \ anteroposterior • 0087 



t transverse 0077 



Diameters m'" ii \ anteroposterior 0115 



t transverse 008 



Ticholeptus beds, Deep river, Montana. J. C. Isaac. 



