E. L. Troxell — Entelodonts in Marsh Collection. 433 



usually large mental tubercles, both anterior and pos- 

 terior ; the very short symphysis ; the deep rami set closely 

 together ; the single-rooted P\ and very small two-rooted 

 P 2 ; the large P 3 and the broad P 4 with a short narrow 

 heel, and finally the well developed talonids on the lower 

 molars. 



Peterson has put this species under Pelonax Cope; it 

 resembles the type, P. ramosus, in having a single-rooted 

 first premolar and in possessing very large tubercles on 

 the jaw, but it is about one sixth smaller and has a double- 

 rooted second premolar. In spite of this great difference, 



Fig. 15. — Megachcerus zygomaticus, gen. et sp. nov. Genoholotype. Cat. 

 No. 10008. Side view of skull, injured, by crushing, showing the enormous 

 extension of the malar bone. One-fifth nat. size. 



it is probably nearer to Pelonax than to any other desig- 

 nated genus. 



P. bathrodon resembles Cope's published description of 

 P. ramosus in size and in the high anterior tubercles. 



Megachcerus zygomaticus Group. 

 Megachcerus zygomaticus, gen. et sp. nov. 



Genoholotype, Cat. No. 10008, Y. P. M. % Upper Oligocene, South Dakota 

 bad lands. 



In addition to the fact of its great size, this unusual 

 elothere (figs. 15, 16) has the relatively largest dependent 

 process of described specimens. In its extreme breadth 



