OKEODON. 55 



Comparison hehoeen Oreodun Culbertsonii and Oreodon gracilis. 



Besides the great disproportion in size between Oreodon Ctdbertsonii and Oreodon 

 gracilis, (the latter being nearly one-third less than the former,) there are other 

 diflferences which, though slight, are important. 



In Oreodon Ctdbertsonii, the sagittal crest rises from the sides of the temporal 

 foss^ in a gradual pyramidal manner ; but in Oreodon gracilis, the intertemporal 

 region at its upper part is more arched, and the sagittal crest rises from it in the 

 form of a thick, abrupt, rugged, linear ridge. 



In the latter species the lachrymal depressions are relatively less deep, and the 

 entrance of the orbits more nearly circular. 



The posterior convergent extremities of the ossa nasi terminate more abruptly 

 in Oreodon gracilis; or in this they are convex and in Oreodon Culbertsonii are 

 angular. 



The ossa tympanica are relatively much more inflated in Oreodon gracilis; and 

 the prominent ridge continuous from them to the auditory process in Oreodon 

 Culbertsonii, is but feebly developed in the former species. 



Oreodon major, Leidy. 



(Pl. IV., Fig. 6.) 

 Syn. Merycoidodon major. 



A third species of Oreodon with some hesitation is proposed upon a fragment of 

 the right side of the upper jaw, containing the true molars, from the collection of 

 Dr. Owen. 



The specimen belonged to a middle-aged individual, as indicated by the tritura- 

 tion to which the teeth have been subjected in mastication; the characteristic 

 enamelled grinding surface of the first true molar being quite obliterated. 



The teeth correspond closely in form with those of Oreodon Culbertsonii, but 

 they are much larger than any of the specimens which have been attributed to the 

 latter. 



It is not improbable, that upon further investigation, the specimen may prove 

 to belong merely to a large variety of Oreodon Cidbertsonii, for the difference in 

 size of the teeth from those indicated in the specimen 10, of the latter species, is 

 not as great as that existing between the teeth of this and those of specimen 16. 



MEASUREMENTS. 



Inches. Lines. 



Length of series of upper true molars ....... 2 84 



Antero-posterior diameter of the last molar ....•••! 



Breadth anteriorly ........••■ H 



