972 THE JOHN DAY FAUNA. 



animals. They resemble considerably the teeth of some of the Dinosauria; 

 for instance, those of the Triassic Clepsysaurus. The sectorial apparatus is 

 especiall}^ effective, and no tissue could long resist the combined action of 

 the opposing blades of the two jaws. Nevertheless, this species did not, 

 probably, attack the large Merycochoeri of the Oregon herbivores, for their 

 superior size and powerful tusks would generally enable them to resist an 

 enemy of the size of this species. They were left for the two species of 

 Pogonodon, who doubtless held the field in Oi-egon against all rivals. The 

 compressed mandibular rami of the Nimravus gompJiodus, though less slender 

 than those of the Archcelurus debilis, are not so well calculated to resist lat- 

 eral strains as the more robust jaws of the majority of the existing Felidoe. 

 History. — The first notice of this species was based on a mandible. As 

 it is exceptionally without tubercular tooth, I referred it to the genus Hop- 

 lophoneus; and since its proportions are very similar to those of the Pogonodon 

 brachyops, of which no mandible had been found up to that time, I identi- 

 fied it with that species. The reception of other specimens enabled me to 

 distinguish the genus Nimravus, but it was not until some time later that I 

 became satisfied that it was distinct from the species to which I originally 

 referred it. The reasons for this conclusion are given under the head of 

 Pogonodon hrachyops. 



Nimravus confertus Cope. 



Bulletin U. S. Geol. Survey Terrs., VI, p. 172, Feb., 1861. American Naturalist, 1880, p. 849, fig. 10. 



Plate LXXI a; lig. 17. 



This species is as yet represented by a mandibular ramus only. It is 

 one-third smaller than that of N. gompliodus. 



The inferior border of the ramus is broken off, excepting for a space 

 belowthe diastema. The general form is narrow, as in N. gompliodus, and 

 there is a projecting ledge along the inner base of the sectorial similar to 

 that seen in the latter species. The angle separating the side from the front 

 of the ramus is rather stronger than in N. gompliodus, but there is no indi- 

 cation of an inferior flare. The diastema is shorter than in the ty]Dical 

 species, its length equaling that of the base of the third (first) premolar; 

 in N. gompliodus it is half as long again. The symphysis is correspondingly, 

 shorter, ceasing a little in advance of, and at the posterior border of, the 



