336 E. L. Troxell — American Bothriodonts. 



Titanotherium beds near Deadwood, South Dakota ; and 

 A. americanus (Leidy) , as reported by Hay den, was found 

 in association with Titanotherium remains. The age of 

 the genus, therefore, is near the border line of the Middle 

 and Lower Oligocene. 



Generic characters. — Of the foreign types JEpinacodon 

 resembles most Hyopotamus {H. hovinus Owen), but from 

 this it can be distinguished by the curved transverse 

 groove and the resulting decrease in size of the hypocone, 

 by the closer grouping of the cusps transversely, by the 

 narrower mesostyle, and by the greater relative length 

 of the molars antero-posteriorly. H, vectianus Owen 



Fig. 6, — Mpinacodon deflectus (Marsh). Holotype. Cat. No. 11802, 

 Y. P. M. Cro-^Ti view of upper molars and premolars. X l/^- 



resembles Elomeryx in some respects more closely than 

 it does the new genus. 



As compared to Bothriodon Aymard, one has difficulty 

 in finding the resemblances ; these distinctions, however, 

 may be noted : the unreduced premolars, and absence of 

 diastema behind P^, the curved transverse valleys of the 

 molars, their narrower outer borders, the grouped cusps, 

 the rougher character with an abundance of tubercles and 

 cingula, the less elongated muzzle, the less forward 

 position of the posterior nares, the more completely 

 inclosed orbit, and the narrow supra-occipital of ^pina- 

 codon. 



As distinct from Elomeryx, ^^ the upper molar teeth 

 have squared outer edges, the styles are more nearly 

 equal, the cusps are tall and sharp, the deuterocone of P* 

 is a cone, not a crescent, the teeth are all much more 

 rugose, with numerous cusps and cingula, P^ is generally 



^® See under Octacodon and Heptacodon the distinctions of ^pinacodon 

 from these genera. 



