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 fosse 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 bulle 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. Kaup. 
MACHAIRODUS PRIMAEVUS. Leidy and Owen.+ 
| (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 neogzeus. 
Lateral view.—(Tab. xii. A, fig. 5.) The temporal fossee 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 
_. * Proce. Acad. Nat. Sci., vol. v., 121. + Ib. p. 329. 
