950 THE MIOCENE FAUNA. 



Hoploplioneiis. The heel, on the other hand, remains throughout the entire 

 family. The anterior basal lobe of the superior sectorial has the same his- 

 tory, its absence being characteristic of the inferior Carnivora, and of all 

 the genera of Nimravidce except Hoplophonevs, where it is rudimental. It is 

 well developed in Drepanodon as in recent Felidce, and is sometimes double 

 in Smilodoii. (8) The development of the inferior flange and latero-ante- 

 rior angle of the mandibular ramus. There is a successive advance in the 

 development of these characters, beginning with the second group, for in 

 the first they are wanting. The latero-anterior angle is developed in Ar- 

 chcclurus and allied genera, and is merely continued on the inferior border 

 of the ramus. In the third group it is much more acute, and is deflected 

 downwards, forming the well-known flange of the saber-tooths. It is long- 

 est in the EusmUus bidentatus Filh. (9) The highest genera of Nimravidce, 

 e. g. Hoplophoneiis, difi'er from true Felida' in the absence of the cutting 

 lobes on the posterior edges of the crowns of tlie larger premolar teeth. 

 But, according to Filhol, these lobes are present in the generalized genera 

 Procelurus and Psendoelurus, which are thus brought into a relation with 

 the Felidce not possessed by the Nimravidce. 



A characteristic perfection of the Felidce is seen in the genus SmUodoti; 

 that is, the vertical direction of the ungual phalanges, by which the claws 

 become retractile. This is well displayed by the two splendid specimens 

 of Smilodoii necator from Buenos Ayres, which have been preserved.^ Un- 

 fortunately, these phalanges have not yet been described in any species of 

 the Nimravidce, and it is not yet certain what their structure really was. 

 Among the true Felidce the genus Cyncelurus displays a less degree of devel- 

 opment in this respect than the other genera, the ungual phalanges lacking 

 the proxunal process below the articular facet. Such a condition is to be 

 looked for among the less perfect genera of Nimravidce. 



The succession of genera above pointed out coincides with the order 

 of geologic time very nearly. Those belonging to groups first and second 

 belong to the Lower and Middle Miocene, except ^lurogale, which is per- 

 haps Upper Eocene, and Pseudcelurus, which is Middle Miocene. The 

 genera of the third division have the same Lower Miocene age, except Eiismi- 



' See American Naturalist, December, 1880, fig. 12. 



