38 



branches were so numerous as to confuse the line. It is clear, 

 however, that from the close of the Cretaceous to the Post- 

 Tertiary, the Bunodont Artiodactyles were especially abun- 

 dant on this Continent, and only recently have approached 

 extinction. 



The Selenodont division of the Artiodactyles is a more 

 interesting group and, so far as we now know, makes its first 

 appearance in the upper Eocene of the West, although forms, 

 apparently transitional, between it and the Bunodonts occur in 

 the Dinoceras Beds, or middle Eocene. These belong to the 

 genus Homacodon, which is very nearly allied to Helohyus and 

 but a single step away from this genus toward the Selenodonts. 

 By a fortunate discovery, a nearly complete skeleton of this 

 rare intermediate form has been brought to light, and we are 

 thus enabled to define its characters. Several species of 

 Homacodon are known, all of small size. This primitive 

 Selenodont had forty-four teeth, which formed a nearly con- 

 tinuous series. 



The molar teeth are very similar to those of Helohyus, but 

 the cones on the crowns have become partially triangular in 

 outline, so that when worn, the Selenodont pattern is clearly 

 recognizable. The first and second upper molars, moreover, 

 have three distinct posterior cusps, and two in front; a peculiar 

 feature, which is seen also in the European genera Dichobune 

 and Cainotherium. There were four toes on each foot, and the 

 metapodial bones were distinct. The type species of this genus 

 was about as large as a cat. With Helohyus, this genus forms 

 a well marked family, the Helokyidoe. 



In the Diplacodon horizon of the upper Eocene, the Seleno- 

 dont dentition is no longer doubtful, as it is seen in most of 

 the Artiodactyla yet found in these beds. These animals are 

 all small, and belong to at least three distinct genera. One of 

 these, Eomeryx, closely resembles Homacodon in most of its 

 skeleton, and has four toes, but its teeth show well marked 

 crescents, and a partial transition to the teeth of Hyopolamus, 

 from the Eocene of Europe. With this genus, is another 



