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



heavy double-rooted tooth strongly sloping backward. 

 P 4 also is a heavy tooth, with rather a small protocone 

 bounded before and behind by definite shelves. 



The first molar is much smaller than the others, but they 

 are all similar in form, having strong fifth cusps or heels. 

 The valleys are rather wide open, and the anterior tuber- 

 cles, like those of Arcliceotlierium, are high. The anterior 

 and posterior halves of the tooth in each case are about 

 equal in width. A small diastema, 9 mm., separates Ci 

 from Pi ; Pi and P 2 are separated about 32 mm. 



The jaw is very narrow as measured across the dias- 

 tema behind P 1? 79 mm. ; the symphysis is relatively short, 

 158 mm., but the rami are deep relative to their length; 

 the depth below P 2 is 92 mm. and that below M 2 , 106 mm. 



Pelonax bathrodon (Marsh) Peterson. 



Holotype, Cat, No. 12030, Y. P. M. 



This species (PI. I, B) was originally referred to Am- 

 modon by Marsh (1893, p. 410, pi. IX), but it differs from 



Fig. 14. — Pelonax potens (Marsh) Peterson. Holotype. Cat, No. 12042. 

 Crown view of lower jaws. One-fifth nat. size. 



the paratype of A. leidyanus in being considerably 

 smaller, and in having high anterior tubercles and broad 

 transverse valleys ; it closely corresponds to the size 10 of 

 the type of the genus Pelonax Cope, and resembles it in 

 many respects, including the possession of a strong pos- 

 terior heel. 



Summary of Pelonax potens Group. 



This group takes for its center the holotype of Marsh's 

 P. potens, of which the principal features are: the un- 



10 Peterson (1909) has made an error in representing the type of P. 

 ramosus Cope as about one-half that shown by Cope. 



