No.7.] NIMRAVID^ AND CANIDiE OF THE MIOCENE PERIOD. 1G9 



development of tlie inferior flange and latero-anterior angle of the man- 

 dibular ramus. There is a successive advance in the development of 

 these characters, beginning with the second groui), for in the first they 

 are wanting. The latero-anterior angle is developed in Archcelurus 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 down- 

 wards, forming the well-known flange of the saber-tooths. It is longest 

 in the Eusmilus hidentatus Filh. (9) The highest genera of Nimravidce^ 

 «. g. Hoplophoneus, differ from the true Felidce in the absence of the cut- 

 ting lobes on the posterior edges of the crowns of the larger premolar 

 teeth. But, according to Filhol, these lobes are present iu the generalized 

 genera Procelurus and Pseudcelurus, which are thus brought into a re- 

 lation with the Felidce not possessed by other Nimravidce. 



A characteristic perfection of the Felidce is seen in the genus Smilo- 

 don ; 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 Smilodon necator from Buenos Ayres, which have been 

 preserved.* Unfortunately, these x>halanges have not yet been de. 

 scribed 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 development in this respect than the other 

 genera, the ungual phalanges lacking the proximal process below the 

 articular facet. Such a condition is to be looked for among the less per- 

 fect genera of Nimravidce. 



The succesion of genera above pointed out coincides with the order 

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

 ond belong to the Lower and Middle Miocene, except JElurogale, which 

 is perhaps Upper Eocene, and Pseudcelurus, which is Middle Miocene. 

 The genera of the first group of division third have the same Lower 

 Miocene age, except Eusmilus, which has been found in the same forma- 

 tation (Phosphorites) as the JElurogale. Brepanodon is Upper Miocene, 

 and Smilodon is Pliocene. 



The relations of these genera are very close, as they differ iu many 

 cases by the addition or subtraction of a single tooth from each dental 

 series. These characters are not even always constant in the same 

 species, so that the evidence of descent, so far as the genera are con- 

 cerned, is conclusive. JSTo fuller genealogical series exists than that 

 which I have discovered among the extinct cats. 



As to the phylogeny of this family, there are flesh-eaters of the Eocene 

 period which may well have been the ancestors of both the Nimravidce 

 and Felida^A I have suggested that this position is most appropriately 

 held by the Oxycenidce, a family of several genera, which included the most 

 formidable, rapacious mammals of that early period in both continents. 



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



tSee On the Genera of the Creodonta, by E. D. Coiie, Proceed. Amcr. Philos. See. 

 July, 1880. 



