234 THE INTERNATIONAL MONTHLY, 
long, much more so than in the pigs, and the feet have only two 
toes each, the only known example of such extreme reduction in 
the whole sub-order. Altogether, these must have been among 
the most curious and grotesque looking animals of their day. 
No direct ancestor of the elotheres has yet been discovered, but 
nearly allied forms occur in all the horizons from the Wasatch 
to the Uinta, which makes it probable that the group originated 
in North America. 
Nothing is yet known concerning the origin of the hippopot- 
amus ; it is first found in the Pliocene of India, but it had 
already attained substantially its present condition. The group 
never reached the western hemisphere, though spreading all over 
Europe and Asia; since the Pleistocene it has been confined to 
Africa. 
The second sub-order of the artiodactyla, and one to which 
an unusual degree of interest attaches, is that containing the 
camels and llamas (Tylopoda). It spite of the fact that no rep- 
resentative of the sub-order is found in this continent, at the pres- 
ent time, it is, nevertheless, a most characteristically North 
American group, and was for ages entirely confined to that 
region, where it attained an extraordinary degree of development 
and diversification ; imitating in a wonderful way the true rumi- 
nants of the Old World and taking their place in North America. 
The true ruminants did not gain a permanent foothold in the 
western hemisphere until the upper Miocene. Many diverging 
and branching lines of the Tylopoda may be traced through a 
longer or shorter course of the American Tertiary, but only one 
of these lines has persisted to the present time, and this is likewise 
the only line which has been found outside of North America. 
For this reason it may be called the main series or line. 
This main series begins in the Wasatch with a very small 
animal {Trigonolestes) hardly larger than a rabbit, which, unfortu- 
nately, is still very incompletely known. The dentition, which 
was first discovered separately, is so like that of many of the 
smaller clawed mammals, that no one could have imagined that 
it belonged to an artiodactyl at all. The subsequent discovery 
