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



the absence of the mental tubercles are characters found 

 elsewhere only in specimens of Dinohyus. 



Ammodon leidyanus (Marsh) (PL III, C) was a species 

 made by Professor Marsh on two teeth from the Miocene 

 of New Jersey, and probably represents the largest of the 

 entelodonts known. It is only mentioned here with the 

 Oligocene forms because of its connection with the larger 

 species. The holotype is Cat. No. 12040, and the paratype 

 Cat. No. 12041, of the Yale collection. 



Dinohyus hollandi Peterson is a very large Miocene 

 species of which the whole skeleton is known. It is so 

 fully and completely described by the author in his inter- 

 esting memoir that any further mention here would be 

 superfluous. 



To the species already listed, the following new desig- 

 nations will be added in later pages, based on characters 

 summarized under their respective groupings : 



ArchcBotherium marshi, sp. nov., figs. 10-12. 



A. clavus darbyi, subsp. nov., figs. 4-8. 



Megachoerus zygomaticus, gen. et sp. nov., figs. 15, 16. 



M. latidens, sp. nov., figs. 17, 18. 



Choerodon caninus, gen. et sp. nov., figs. 19, 20. 



The Bony Processes in Relation to the Teeth and 



Muscles. 



The teeth are so constructed that they interlock 

 throughout ; the long separation of the incisors from each 

 other and from the canines, to make way for the opposing 

 teeth, is noteworthy, but the premolars also interlock : P 4 

 fits into the inner side of P 3 - 4 in a triangular pocket; the 

 posterior shelf of P 4 comes in contact with the top of the 

 fourth upper premolar. This strong cutting machine, 

 represented by the formula PJ£ , was well adapted to 

 nipping off a particularly tough root, done by a backward, 

 inward shearing of the lower jaw ; and to fortify the teeth 

 for this backward pressure, the lower premolars face in 

 that direction, while the upper teeth are set at an angle 

 facing forward. 



The molars are constructed to mash the food, which 

 probably consisted of bulbs and roots torn up by the 

 canines and cut off and into short lengths by the pre- 

 molars. The high cusps of M 2 and M 3 fit in between the 

 cones respectively of M 1 - 2 and M 2 - 3 ; there is just room 



