Thorpe — New Genus of Oligocene Hycenodontidce. 279 



The total skull length is 345 nun., and the length from the 

 prosthion to the occipital condyles inclusive is 318 mm. 

 The bone is very heavy and massive, and in places quite 

 rugose, as, for example, on the postorbital processes of 

 the frontals. 



The condition of wear of the teeth is noteworthy in that 

 it shows such marked differential abrasion. One of the 

 most interesting conditions is shown by the left P 4 which 



Fig. • 2. — Neohy amotion 

 X about 1/3. 



liorridus (Leidy). Left naif, palatal view. 



now consists of but three rounded stumps, the entire 

 crown having been worn away, while the left M 1 , although 

 considerably worn, yet descends at least 15 mm. below the 

 surface of P 4 . On the same side, the P 3 shows about twice 

 as much wear on the anterior half, or it is worn so that the 

 crown has a decidedly oblique surface sloping forward 

 and upward. Both P 3 are placed obliquely in the maxil- 

 lary, with the anterior part inward. All of the superior 

 teeth are crowded, except both P 1 , which are isolated, the 

 minimum diastema being posterior, with a diameter of 

 4 mni. 



All of the inferior teeth are crowded, except P x . The 

 third lower molar has a very effective shearing surface, 

 although the crown is considerably shortened vertically 

 by wear, so that all trace of the fore and aft divisions is 

 obliterated and the remaining surface is one long, nearly 

 level blade. The second lower molar is low and rounded, 

 with no trace of a shearing surface, while Mj consists of 

 two rounded stumps nearly level with the alveolar parapet. 

 The contrast is quite striking between this stump of M x and 

 the almost unworn contiguous right P 4 , extending upward 

 21 mm. higher than M. t . The length of the symphysial 

 suture is 116 mm. This great length is a compensatory 

 mechanical device for overcoming the slenderness of the 



