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



names Machcerodus and Drepanodon. Dinotomius atrox 

 Williston is a synonym of R. occidentalism as has been shown 

 by the writer (Amer. Nat., January, 1896). 



The genera Archoelurus and Nimravus have remained as 

 first defined. 



Our knowledge of North American fossil forms of the true 

 Felinge is very limited. Leidy has described Pseudazlurus 

 intrepidus, referring it to the European genus established by 

 Gervais. There are several imperfectly known species of 

 Felis. Leidy has described F. atrox and F. augustus. Felis 

 imperialis Leidy is not sufficiently characterized to be retained. 

 Scott has described % F. maxima from a humerus found in the 

 Loup Fork of Kansas. It will be remembered that remains 

 from that deposit have been described under the genus 

 Machcerodus, and it is not probable that this humerus belongs 

 to a different genus although further material must be found 

 before the affinities of these forms can be determined. The 

 genus Uncia Gray cannot be distinguished with certainty in 

 fossil forms and is here included in Felis. 



The Dentition of the Felidce. 



The modifications of the dentition of the Felidse consist, on 

 the whole, of the reduction of the number of teeth until 

 almost the entire function of the molar series is performed 

 by a single large sectorial in each jaw and, accompanying 

 the reduction in number, an increase in size and complexity 

 of structure whereby the-individual teeth become more perfect- 

 cutting instruments.* 



The specialization of one tooth as a sectorial to the ex- 

 clusion of the others appears to be due to the following causes. 

 It is to be observed that when a cat devours a carcass it cuts 

 off masses by a shearing action of the jaws. In so doing the 

 part to be divided is brought to the canthus or angle of the 

 soft wall of the mouth, which is just at the front of the 

 masseter muscle, at which point the greatest amount of force 

 is gained, since the weight is brought immediately to the 

 power. The first inferior molar situated at this point can be 

 most effectively used and has developed into a sectorial. In- 

 asmuch as the inferior and superior teeth do not directly 

 oppose each other but form an alternate series, the first inferior 

 molar more nearly opposes the last upper premolar and this 

 tooth has become the superior sectorial. The shortening of 

 the jaw which accompanied the reduction of the molar series 

 has brought the canines nearer to the powerful muscles of 

 mastication and they are as a result more effective weapons in 

 the Felidae than in other carnivores. 



* Origin of Specialized Teeth of the Carnivora, Cope, Amer. Nat., p. 171, 1879 ; 

 Mechanical Genesis of Tooth-forms, Ryder, Proc. Acad. Nat. ScL, 1878. 



