8 
the same conclusion in both, by the same stages. The primitive 
form of the Macherodont line represented by Hoplophoneus has 
its extreme in Husmilus, where the second inferior premolar and 
an incisor tooth are wanting, giving a formula of I. 2,C.1; Pm. 
1; M.1. In Macherodus 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 reiated to Macherodus, as Husmilus to 
Hoplophoneus. In the Feline line proper, on reaching the exist- 
ing genera, we have lost the heel of the inferior sectorial 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 Macheer- 
odont line, is the loss of the interior tubercle of the superior 
sectorial, which characterizes the genus Cynelurus. 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 C. jubatus. 
As already remarked, the genera of the Machzrodont 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 
part 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 
