a 3 8 THE INTERNATIONAL MONTHLY. 
Day, and die out at the end of the Loup Fork. Some of these 
were very small animals, closely resembling the so-called "mouse 
deer " of the East Indies, and none of them were large. One 
of the most curious and characteristically American of these side 
branches, which was apparently given off from the main tylopo- 
dan stem in the middle Eocene, is the family of the oreodonts. 
In the Uinta this family is already distinctly separated. The 
oreodonts were short necked, short limbed and footed animals, 
having much the proportions of the peccaries, but differing in 
the presence of a long and heavy tail ; and they must have 
swarmed in vast herds all over the western plains, for they are by 
far the commonest of Oligocene and Miocene fossils. Some of 
the later representatives of the family grew to a much greater 
size than its earlier members, although none of them can be called 
large. Some of the genera developed a proboscis, some became 
adapted to an aquatic life, and several were very bizarre in appear- 
ance ; but the amount of structural change that they underwent 
is comparatively small. For example, nearly all of them retain 
the full number of teeth ; in none are the limbs or feet elongated, 
or any of the limb bones suppressed or coossified, and in none is 
the number of toes less than four. After the Loup Fork all 
traces of the family disappeared. 
An extraordinary side branch of the oreodonts, which was given 
off in the Uinta, is the agriochoerid family, which dies out after 
the John Day. The skull, limbs, and feet of these wonderfully 
curious creatures, discovered at different times and places, were 
at first referred to no less than three different orders of mammals, 
until the finding of complete skeletons showed that they all 
belonged to the same animal. No one could have predicted such 
an association of parts. With skull, back bone, and teeth resemb- 
ling those of the oreodonts, these animals have developed claws 
instead of hoofs, which is not paralleled in any other group of 
artiodactyla. 
The Pecora, or true ruminants, form the third sub-order 
of the Artiodactyla. This is a group of Old World origin 
and the one which represents the highest grade of artiodactyl 
