DAKOTA AND NEBRASKA. 99 



Oreodon major. 



From a few small fragments of jaws with teeth it was early suspected that there 

 was a third species of Oreodon, larger than the preceding, to which the above name 

 was given. The subsequent examination of large collections of remains of Oreodon 

 Cidbertsoni, from the variations observed in different skulls of this species, led to the 

 opinion that the specimens originally referred to 0. major also belonged to the same. 

 The collection of Dr. Hayden from the Mauvaises Terres of White River contains 

 an almost entire skull, without the lower jaw, which confirms the view of the 

 existence of a third and larger species of the genus, to which the name of Oreodon 

 major must still be retained. The fine specimen proving the existence of this species 

 is represented in figure 1, plate VII, and in those of plate VIII. 



The skull is. about a fifth larger than that of 0. Cidbertsoni, or about twice the size 

 of that of (^ gracilis. In general form, proportions and details of structure it 

 approaches closely that of the latter species. 



The cranium is more constricted immediately in advance and in the course of the 

 border of the squamosals than is sometimes observed in 0. Oulhertsoni. The sagittal 

 crest is not only stronger in relation with the size of the skull, but also higher, 

 especially at its fore part, than in the other species. It bifurcates in front, and 

 includes a triangular notch for the reception of the summit of the frontals. Its pos- 

 terior extremity, as in the other species, forms, together with the summit of the 

 occipital, a triangle, with the basal angles extended as a pair of diverging semi- 

 circular plates upon the sides of the inion. 



The forehead is transversely convex, and not depressed along the middle except at 

 the summit of the frontals, which are co-ossified at their posterior third. The supra- 

 orbital foramina are relatively as much separated as in 0. gracilis, and the grooves 

 from them are comparatively feeble. 



The orbits are small, being absolutely no larger than in 0. Culberfsoni. They are 

 vertically slightly oval. The lachrymal fossaa in advance are relatively shallower 

 than in the latter species, and do not extend to the anterior border of the lachrymal 

 bones. 



The face has the proportions of the more robust varieties of 0. Calbertsoni. The 

 upper part is transversely convex. The nasal bones are broad, and their posterior 

 extremities together form an acuminate triangle, eighteen lines long and fourteen 

 wide. 



The most striking anatomical peculiarity in the skull of 0. major, — one that could 

 not have been anticipated from its general resemblance to the skulls of the other 

 species, — is the comparatively enormous size of the auditory bulla. In 0. Cidbertsoni 

 this is not only of very small size compared with its condition ia ruminants 



