1880. | On the Extinct Cats of America. 839 
which the claws become retractile. This is well displayed by the 
two splendid specimens of Swzlodon necator from Buenos Ayres, 
which have been preserved (See Fig. 12). Unfortunately, these pha- 
langes have not yet been discovered in any species or the Mimra- 
vide, and it is not yet certain what their structure really was. 
Among the true Felde, the genus Cynælurus 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 perfect 
genera of Mimravide. 
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 
<Elurogale, which is perhaps upper Eocene, and Pseudelurus, 
which is middle Miocene. The genera of the first group of di- 
vision third, have the same lower Miocene age, except Eusmilus, 
which has been found in the same formation (Phosphorites) as the 
` Alurogale. 
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 conclusive. No 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 Mimravide and Felide I have suggested that this position 
is most appropriately held by the Oxyenide, a family of. several 
genera, which included the most formidable rapacious mammals 
of that early period in both continents. The interval between 
them and the Mimravide is however great, for in the Oxyenide 
when there is a sectorial tooth of the upper jaw, the first true mo- 
lar is utilized instead of the last premolar; 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 oy ig! me = Felide were de- 
rived from the genus Proe/ui seudelurus, if indeed th 
two genera be not the primitive members of that family, for as above 
*See, On the genera of the Creodonta, by E. D. Cope; Proceed. Amer. Philos. Soc. 
July, 1880. 
