438 G. I. Adams — Extinct Felidce of North America. 



Eusmilus in the reduction of the dental series, and with this 

 form they become extinct although it is probable, judging from 

 fossil remains, that the dominant genus in Pleistocene times was 

 Smilodon. 



The genera Archcelurus, ^Elurogale and Nimravus seem to 

 represent specialized forms of more primitive genera, forming 

 a side line of development. Of these Archcelurus is most 

 primitive. It is not directly derivable from any known form 

 nor does it stand ancestral to the genera of Machserodonts 

 previously discussed. The superior sectorial consists of a prin- 

 cipal and a posterior cusp. There is a slight convexity in the 

 position occupied by the anterior basal cusp in Hoplojphoneus. 

 The same thing is seen in Nimravus, but it does not develop 

 into a true cusp. The principal cusp has a convex internal 

 buttress as in Hoplophoneus. The inferior sectorial consists of 

 an anterior, principal and posterior cusp or heel. From this 

 genus JElurogale could be derived by the loss of the first 

 superior premolar. There is also a different development of 

 the canine, the tooth becoming longer, recurved and acquiring a 

 posterior denticulate margin. Nimravus differs in dental 

 formula from JElurogale in the loss of the second inferior 

 premolar. The canine, however, is the most striking feature 

 of this genus : it is nearly straight and spike-shaped, a form 

 which is seemingly not derivable from JElurogale but rather 

 from Archcelurus. ^Elurogale is a European genus and 

 although indicative of the order of reduction of the teeth in 

 this small and seemingly aberrant group, it cannot be said to 

 occupy an intermediate position between the other two genera. 

 These three genera differ from other Machaerodonts in the 

 order of reduction of the teeth, all having retained the second 

 inferior molar. This tooth is, however, on the point of disap- 

 pearing in Nimravus, as is indicated by its absence on one side 

 in a second specimen of N. gomjphodus. Archcelumts exhibits 

 a peculiarity which should not be overlooked, in the strange 

 deflection or exostosis of the border of the mandible posterior 

 to the molar series. Of this a trace is seen in Nimravus. 



Of the true cats there is but one genus which is known only 

 as an extinct form, namely Pseudo&lurus. Felis, Lynx and 

 Cyncelurus, however, are known as fossils. Pseudwlurus 

 presents the most primitive dental formula and one which can 

 be compared with Dinictis as regards tooth structure, but 

 it differs in the absence of the second inferior molar. 

 Pseudcelurus probably gave origin to Felis through the loss 

 of the second inferior premolar. Cyncelurus differs from 

 Felis in the absence of the internal cusp of the superior sec- 

 torial and the somewhat imperfect retractility of the claws. 

 It forms a side development from the main line of descent. In 



