Cope.] 5Ub L j an- 18i 



resenting two crescents, of which the anterior has its posterior horn 

 developed as an obliquely transverse crest directed inwards. Last true 

 molar with a heel composed of two columns. 



In the superior temporary dentition the last premolar has the form of the 

 first permanent true molar. The third premolar has five lobes, i. e., four 

 crescents and an anterior odd one. The other temporary premolar resem- 

 bles that of the permanent series. The last inferior temporary premolar has 

 the three pairs of lobes usual in the Artiodactyla, and the two which pre- 

 cede it resemble the corresponding permanent teeth. Says Leidy : * "The 

 permanent true molars successively protrude and occupy their functional 

 position before any of the deciduous molars are shed. The displacement of 

 the latter by their permanent successors appears to begin with the eruption 

 of the last of these, which is followed by those in advance. The first 

 permanent premolar of the upper jaw appears to have protruded after the 

 deciduous teeth, and occupied a position with them in the functional series, 

 but remains after these are shed. " 



The cranial characters which belong to Oreodon as a genus are the fol- 

 lowing : Orbit completed behind ; temporal fossae separated by a sagittal 

 crest. A lachrymal fossa, but no facial nor frontal vacuities. Premaxil- 

 lary bones distinct from each other and from the maxillaries. Nasal bones 

 well developed. Auditory bullae not inflated. 



The preceding dental and cranial characters have been pointed out by 

 Leidy in his various palseontological works. On account of the absence 

 of the necessary material he was unable to give the characters of the 

 remaining parts of the skeleton. These are of course necessary to a 

 correct estimate of the affinities of the genus, and I will endeavor to add 

 such information as my material will permit. This consists of numerous 

 more or less complete skeletons found in connection with the skulls by 

 myself in Colorado in 1873. 



Vertebra. The cervical vertebrae are rather short, and the character of 

 the articulation of the centra slightly opisthocoelous, and the articular 

 faces are quite oblique. The axis is the longest vertebra ; the three last 

 centra are subequal in length. In one of my series the seven cervicals 

 are preserved. In all of these, excepting the seventh, the bases of the 

 diapophysis are perforated by the vertebrarterial canal. In the sixth 

 vertebra, the decurved parapophyses are especially robust. The axis and 

 three succeeding centra display strong hypapophyses at their posterior ex- 

 tremities, which are carried forwards as strong median keels. The odon- 

 toid process is depressed so as to have a lenticular section ; it is not exca- 

 vated above, but in my largest specimen the internal borders of the facets 

 for the atlas are continued so as to enclose a short groove on each side at 

 its base. In one smaller and immature specimen this is wanting. The 

 vertebrarterial canal of the axis is enclosed as in the other cervicals. The 

 canal for the second spinal nerve has a narrow roof, but there are no canals 



* Ancient Fauna of Nebraska, p. ii. 



