564 



MACHAIRODUS OF NEBRASKA. 



size of the pars squamosa of its temporal bones. Since the description of the 

 specimen the corresponding portion of the head of Oreodon has become known, 

 between which there is a great degree of resemblance. In both genera the pars 

 squamosa is very large, the temporal fossae unite at the top of the cranium upon a 

 sagittal crest, and the parietal bones, which are very narrow between the tops of 

 the temporal bones, are also very much advanced in their position. In both, also, 

 the glenoid articulation is nearly transverse, but in Eucrotaphus the post-glenoid 

 tubercle is very much thicker. In this, also, the os tympanica forms a large audi- 

 tory bulla, while it is reduced to little more than a prominent crest in Oreodon. 



In Dr. Owen's collection is a corresponding portion of a cranium (Tab. xv., 1, 2) 

 to that described of Eucrotaphus Jacksoni, but it is rather larger, and probably 

 indicates a distinct species. In it the auditory bullae are not simply mammillary, 

 as in E. Jacksoni, but are laterally compressed ovoidal. For this second species, 

 the name Eucrotaphus auritus is proposed. 



Nothing is certainly known of the dentition, or of the anatomical characters of 

 the face of Eucrotaphus. 



I suspect from the relation of size of the described fragments of the latter to the 

 jaws of Agriochcerus,* and the general resemblance of the true molars of this to 

 those of Oreodon, that the former two are really one and the same genus ; but to 

 determine this with certainty it must be left for further discovery. 



MACHAIRODUS. Simp. 

 MACHAIRODUS PRIMiEVUS. Leidy and Ckoen.-f 



(Tab. xii. a, fig. 5.) 



Of this species Dr. Owen's collection contains a much fractured head, with the 

 symphysis of the lower jaw, zygomata, and ends of the nasal bones broken away. 

 Portions only of both superior canines, much fractured, remain in the specimen. 

 The superior incisors were lost originally, and the alveoli are filled by matrix. 



The cranium is one-fourth less in size than that of the Panther, Felis concolor, 

 or about half that of Machairodus neogaeus. 



Lateral view. — (Tab. xii. A, fig. 5.) The temporal fossae are relatively shorter 

 and vertically deeper than in the Panther, and have a very much greater extent of 

 surface anterior to a line drawn vertically from the glenoid cavity, and very much 

 less posteriorly. A very large surface for attachment of the temporal muscle is 

 also formed upon the post-orbital process, and the whole disposition of the temporal 

 surface is to give a more vertical direction of the fibres of the temporal muscle in 

 their course to the coronoid process than exists in the Panther and other species of 

 Felis. 



The para-mastoid and mastoid processes are combined into an oblique process an 



* Proc. Acad. Nat. Sci., vol. v., 121. 



| lb. p. 329. 



