220 OREODON AND MESOREODON CHAP. 
Aiphodon was a hornless creature, but with only two toes, the 
two lateral digits being represented by the merest rudiments of 
metacarpals. The other metacarpals were unusually long. 
Amphimeryz (also called Niphodontotherium) is much more 
imperfectly known, but belongs to this family or to that of the 
Caenotheriidae. Dichodon is another member of the same family. 
Fam. Oreodontidae.—This family, consisting of numerous 
genera, is limited to the North American continent. Its range 
in time is from the Eocene to the Lower Pliocene. The family 
as a whole is to be distinguished by a number of primitive 
characters. The dentition is complete; the feet are four- or 
even five-toed; the orbit is sometimes open behind. The canines 
of the lower jaw are not more pronounced than the u.cisors. 
The characteristics of the group will be further developed by 
a consideration of some of the principal genera which are in- 
cluded in this family. 
Oreodon is a Miocene form about as large as a Peccary. The 
skull has a short face with a completely-closed orbital cavity. 
In front of the orbit is a deep pit, not a mere deficiency of 
ossification, such as occurs In many Artiodactyles. This is 
placed on the lachrymal bone, and is in fact a lachrymal fossa, 
such as occurs in other forms. The odontoid process of the axis 
vertebra is somewhat cheese-taster shaped, as in recent Artio- 
dactyles. There are fourteen dorsal vertebrae and a very large 
number of caudals. The radius and the ulna are completely 
separated, as are the carpals. There are five digits to the fore- 
limbs. The fibula is complete and independent. The hind-foot 
is four-toed. Several species of the genus are known. 
Merycochoerus is an allied Miocene genus. It is more 
massive in form than the last, but otherwise does not present 
differences of importance. 
Mesoreodon is another genus of this family which presents 
some curious features of organisation. In the skull and teeth 
there is nothing very noteworthy, but the hyoid is remarkable. 
This appendage of the skull is by no means always preserved, 
and when it is, it might be denied that it belonged to any 
particular skull. In the present case there appears to be no doubt 
as to the identity of the bones, which resemble the corresponding 
bones of the Perissodactyla much more than they do those of 
other Artiodactyles. Associated with the bones an ossified 
