DAKOTA AND NEBRASKA. 113 



The back abutment "of the last upper true molar is relatively more robust than in 

 the latter, and forms a process of such strength as to wear away a distinct slope upon 

 the hinder lobe of the corresponding tooth of the lower jaw. 



The first upper premolar is more isolated in its position than in Oreodon, being 

 separated by a comparatively wide interval from the sec6 series, as well as 



from the canine. 



The crowns of the first and second upper premolars are narrower in proportion 

 with their length and bi'eadth than in Oreodon.. In the crown of the third premolar 

 the postero-iuternal lobe, as it exists iu the latter genus, is degraded to the condition 

 of a festooned basal ridge enclosing a pair of mammillary tubercles. 



The first inferior premolar is more crowded in its position than in Oreodon, Ijoing 

 inserted obliquely across the alveolar border, so that one-half of its crown is situated 

 internally to the canine, and a third is exterior to the second premolar. 



The canines are of robust proportions, the inferior being much more so than the 

 superior. Their crown is half worn away. The crown of the superior canine is 

 trihedral, the external surface being invested with enamel. The antero-internal 

 surface is a triangular plane worn by contact with the inferior lateral incisor, and the 

 postero-internal surface forms part of a lozenge-shaped plane worn hy contact with 

 the inferior canine. The latter is a trihedral column, with a trihedral pointed 

 summit forming the remainder of the crown, which is worn off at its fore part into a 

 broad sloping plane by contact with the superior canine. 



The measurements of the specimens, compared with corresponding ones of Oreodon 



major, are as follow : 



M. proprius. O. major. 



Lines. Linea. 



Length of the upper alveolar border, 



Length of the lower a u ... 



Depth of infra-orbital arch, .... 



Distance of infra-orbital margin from the alveolar margin. 

 Distance of infra-orbital foramen from the alveolar margin. 

 Distance from infra-orbital foramen to front of incisive alveoli, 

 Depth of lower jaw at fore part of last molar, 

 Length of symphysis, ..... 

 Length of upper molar series, .... 

 Length of lower molar series, .... 

 Length of upper true molar series, 

 Length of lower " " " . 

 Autero-jiosterior diameter of last upper molar. 

 Transverse " a u _ _ 



15 



