1879.] NATURAL SCIENCES OF PHILADELPHIA. 175 



the same conclusion in both, by the same stages. The primitive 

 form of the Machaerodont line represented by Eoplophoneus has 

 its extreme in Eusmilus, where the second inferior premolar and 

 an incisor tooth are wanting, giving a formula of I. 2, C. I ; Pm. 

 1 ; M. 1. In Machserodus we have the modern characters of the 

 molars seen in Felis, viz., no heel of the inferior sectorial ; the 

 superior sectorial with an anterior lobe, and posterior lobes of the 

 premolars. The extreme of this line is reached in Smilodon, 

 where the second inferior premolar is one rooted or wanting. 

 This genus then stands- related to Machserodus, as Eusmilus to 

 Eopl()})honeus. In the Feline line proper, on reaching the exist- 

 ing genera, we have lost the heel of the inferior sectoiial and 

 gained the posterior lobes of the premolars and anterior lobe of 

 the superior sectorial at once. A further modification of the 

 dentition of the superior series of the recent forms, is seen in the 

 loss of the first superior premolar in Lynx and Neofelis. Still 

 another, which is one step beyond what is known in the Machaer- 

 odont line, is the loss of the interior tubercle of the superior 

 sectorial, which characterizes the genus Gynselurus. A superior 

 sectorial tooth having the character of that of this genus was 

 discovered by Dr. Hayden in the Loup River formation of 

 Nebraska, and was referred to a species by Dr. Leidy under the 

 name of Aelurodon ferox. It was much larger than the G.jubatus. 

 As already remarked, the genera of the Machaerodont line are 

 extinct, and this in spite of the fact that they presented the most 

 perfect weapons of destruction in their canine teeth, from the 

 earliest times. Their other modifications of structure advanced 

 pari passu with those of the Feline series, and, among others, 

 the feet presented in the latter forms at least (e. g., Smilodon 

 necator, Gew.),the most perfect prehensile power of the lions and 

 tigers of to-day. As nothing but the characters of the canine 

 teeth distinguished these from the typical felines, it is to these 

 that we must look for the cause of their failure to continue. Prof. 

 Flower's suggestion appears to be a good one, viz. : that the 

 length of these teeth became an inconvenience and a hindrance to 

 their possessors. I think there can be no doubt that the huge 

 canines in the Smilodons must have prevented the biting off of 

 flesh from large pieces, so as to greatly interfere with feeding, and 

 to keep the animals in poor condition. The size of the canines 

 is such as to prevent their use as cutting instruments, excepting 



