682 THE POPULAR SCIENCE MONTHLY. 



of the larger mammals now living ; and the group dates back at least 

 to the lowest Eocene. Of the two well-marked divisions of this 

 order, the Bunodonts 1 and the Selenodonts, 2 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 primitive 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 

 Suilline 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 supposed to be a Perissodactyle, while Helohyus cer- 

 tainly 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 Ter- 

 tiary, is strewed 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 Parahyvs 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 early Suillines, with the possible ex- 

 ception of Parahyus, appear to have had at least four toes of usable 

 size. 



In the lower Miocene, we find the genus Perchcerus, seemingly a 

 true Suilline, and with it remains of a larger form, Elotherium, are 

 abundant. The latter genus occurs in Europe in nearly the same hori- 

 zon, and the specimens known from each continent agree closely in 

 general characters. The name Pelonax has been applied erroneously 

 to some of the American forms ; but the specimens on which it was 

 based clearly belong to Elotherium. This genus affords another ex- 

 ample of the aberrant Suilline offshoots, already mentioned. Some 

 of the species were nearly as large as a rhinoceros, and in all there 

 were but two serviceable toes ; the outer digits, seen in living animals 

 of this group, being represented only by small rudiments concealed 

 beneath the skin. In the upper Miocene of Oregon, Suillines are abun- 

 dant, and almost all belong to the genus Thinohyus, a near ally of 



1 Bunodont (hill-tooth) ; hence, teeth the crowns of which are composed of rounded 

 tubercles. 



2 Selenodont (moon-tooth) ; teeth which have the crowns marked by crescents. 



