NIMRAVID^. 951 



h(S, which has been found in the same formation (Phosphorites) as the 

 ^Jiirogale. Among Felidce, Drepanodon is Upper Miocene, and Smilodon is 

 Pliocene. 



The relations of these genera are very close, as they differ in 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 concerned, is con- 

 clusive. No fuller ffenealoorical series exists than that which I have discov- 

 ered 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 Niinravidce and 

 Felidce." I have suggested that this position is most appropriately held by 

 the Oxycenidce, a family of several genera, which included the most formid- 

 able, rapacious mammals of that early period in both continents. The inter- 

 val between them and the Nimravidce is, however, great; for in the Oxycenidce, 

 when there is a superior sectorial tooth, the first true molar in the upper jaw 

 is utilized instead of the last pi-emolar, and the second true molar below is a 

 sectorial as well as the first. Several intervening forms must yet be found 

 to complete the connection, if it have ever existed. It is, however, very 

 likely that the true Felidce were derived from the genus Procelurus, through 

 Pseudcehtnis, if indeed these two genera be not the primitive members of 

 that family, for, as above remarked, the evidence of their possession of the 

 characters of the Nimravidce has not yet been obtained. There can be no 

 reasonable doubt that the genera Drepanodon and Smilodon in the Felidce are 

 the descendants of Hoplophoneus and allied genera. In fact, the Nimravidce 

 and Felidce are "homologous groups," having con-esponding terms in the 

 manner I foreshadowed as a general principle in 1 868 (Origin of Genera). 



' JI. Filhol lias sUowu the range of variation in the JElurogale intermedia to he considerable. 

 While the normal dental formula is as given above, molars § J, he believes that it may I'ange to ^ | iu 

 one direction, and i yi or | }, in the other direction. It never attains the formula J i of Arcliwlurus^ 

 while the occurrence of two premolars in the lower jaw is rare. Originally M. Filhol was inclined to. 

 believe that there were three species, and this view is confirmed by the range in size. The largest 

 specimens measure .0t:5 M. ou the alveolar line behind the canine, and the smallest .030, or less than 

 half as long. The discovery of various intermediate sizes led M. Filhol to combine the three species 

 into one. I incline to think M. Filhol's belief in three species to have better foundation thau his 

 belief in hut one. Were the animals living, it is prob.able that their characters would be much more 

 readily defined than is possible with the jaws only. Meraoircs sur quelques MammifSres Fossiles des 

 Phosphorites du Quercy, Toulouse, 18*2. 



= See On the Genera of the Creodoiita, liy E. D. Cope, Proceed. Amer. Philos.. Soc. July, 1880. 



