36 



dates back at least to the lowest Eocene. Of the two well 

 marked divisions of this order, the Bunodonts and the Seleno- 

 donts, as happily defined by Kowalevsky, the former is the 

 older type, which must have separated from the Perissodactyle 

 line, after the latter had become differentiated from the prim- 

 itive Ungulate. In the Coryphodon Beds of New Mexico, 

 occurs the oldest Artiodactyle yet found, but it is at present 

 known only from fragmentary specimens. These remains are 

 clearly Suilliue in character, and belong to the genus Eohyus. 

 In the beds above, and possibly even in the same horizon, 

 the genus Helohyus is not uncommon, and several species are 

 known. The molar teeth of this genus are very similar to 

 those of the Eocene Hyracotherium, of Europe, which is sup- 

 posed to be a Perissodactyle, while Helohyus certainly is not, 

 but apparently a true lineal ancestor of the existing pigs. 

 In every vigorous primitive type which was destined to survive 

 many geological changes, there seems to have been a tendency 

 to throw off lateral branches, which became highly specialized 

 and soon died out, because they are unable to adapt themselves 

 to new conditions. The narrow path of the persistent Suilline 

 type, throughout the whole Tertiary, is strown with the remains 

 of such ambitious offshoots, while the typical pig, with an 

 obstinacy never lost, has held on in spite of Catastrophes and 

 Evolution, and still lives in America to-day. In the lower 

 Eocene, we have in the genus Parahyus apparently one of these 

 short-lived, specialized branches. It attained a much larger 

 size than the true lineal forms, and the number of its teeth 

 was reduced. In the Dinoceras Beds, or middle Eocene, we 

 have still, on or near the true line, Helohyus, which is the 

 last of the series known from the American Eocene. All 

 these eai'ly Suillines, with the possible exception of Parahyus, 

 appear to have had at least four toes, all of usable size. 



In the lower Miocene, we find the genus Perchcerus, seem- 

 ingly a true Suilline, and with it remains of a larger form, 

 Elotherium, are abundant. The latter genus occurs in Europe 

 in nearly the same horizon, and the specimens known from 



