1884.] 551 [Cope. 



The canines are much larger, with cylindrio root and flat, incisor-like 

 crown. The first premolar is still larger, and is of about the same form as 

 the canine, from which it is only separated by a slight divergence of the 

 crowns. There are no diastemata. The second premolar has a compressed 

 triangular crown, with a median ridge on the internal side. Its long 

 diameter is diagonal, running outwards posteriorly. The long axis of the 

 third premolar is similar, while the other teeth are more nearly in line. In 

 the third premolar the fossa interior to the median internal heel is much 

 deeper than that posterior to it. The corresponding fossa is still larger in 

 the fourth premolar, while the crown has a heel in the form of a trans- 

 verse curved crest, separated from the median heel on the inner side by 

 a Assure. The true molars increase rapidly in size posteriorly, but not so 

 abruptly as in the Pithetistes bremfacies. The internal crescents are very 

 fiat, and the posterior edges of their columns project moderately. The ex- 

 ternal crescents are very convex. The prismatic character of the teeth in- 

 creases much posteriorly, so that the roots of the third tooth are short, and 

 the crown long. The enamel is minutely rugose. 



The third superior temporary molar has two pairs of crescents. The an- 

 terior pair are, however, not so well developed as the posterior pair and the 

 two valleys are soon obliterated by wear. The crescents are equal in the 

 fourth temporary molar. The fourth permanent premolar is protruded at 

 least as soon as the third true molar, sooner than the posterior column of 

 the latter. In this it differs from the Oreodon culbertsoni, where the last 

 true molar is protruded first, and is a cotemporary of both the third and 

 fourth deciduous molars ;* and the 0. gracilis, where the last true molar is 

 a cotemporary of the third deciduous. 



In the inferior temporary dentition, the lobes of the last molar are sub- 

 equal, the posterior one being a little the larger. The protrusion of the 

 last true molar is also probably delayed until the shedding of the deciduous 

 series, as in the superior series ; but my specimens are either very young 

 or fully adult, and therefore I cannot demonstrate this point as fully as in 

 the case of the superior series. 



Measurements of Skull. 



M. 



Length from condyle to front of canine inclusive 117 



" " " " otic bulla (axial) 010 



" " " " palatonareal notch, 0575 



" " " " anterior line of glenoid cavity. .038 



Depth of occiput, including condyle 041 



" at middle of orbit, exclusive of teeth 037 



" " infraorbital foramen " " 016 



" " premaxillary border " " 023 



Width at " " above 022 



" between orbits 038 



* Leidy. Ancient Fauna of Nebraska, 1853, p. 51, PI. IV, figs. 1, 2. 



