148 MEMOIRS OF THE CARNEGIE MUSEUM 
found with these parts present in the Oligocene formation have the chin processes 
present. This character then cannot be regarded as only of sexual importance so 
far as the Oligocene forms, which are most abundantly found, are concerned. It 
then remains to be seen whether certain forms like Archxotheriwm clavum with the 
relatively small and posteriorly placed chin-processes led up to such forms as Do- 
don or if we will yet find in the lower Oligocene a form minus these protuberances. 
The discovery of such a form would indicate that the various lines even to quite 
small details of differences were already well established in older Tertiary time. 
While the variation in the canine teeth, the dependent processes of the lower jaw, 
and the jugal of the skull in the different species of the lower Oligocene, may seem 
comparatively small, they are nevertheless of some importance when it is shown that 
certain other parts, as for instance the vertebral column, are quite varied. In 
Archeotherium ingens from the lower Oligocene, the neural arches of the dorsal 
vertebree are imperfectly pierced by canals, while in Archwotherium crassum from 
the same horizon, the horizontal canals are apparently present as in Bos tawrus. In 
Dinohyus from the Miocene we know that the neural arches of the dorsals are not 
only perforated by horizontal canals, but by vertical canals as well; a character 
which is identical with what is found in Sus. 
While the geographical distribution of this family in Asia is at present only a 
matter of speculation, it is clear that Europe and especially North America were 
occupied by it. Thus we have seen that while their remains are comparatively 
abundant on the flanks of the Rocky Mountains, evidence of their existence is not 
altogether wanting in California and New Jersey (“ EZ. superbum,” Ammodon leidy- 
anum). From the lower Oligocene upward, and before the close of the Miocene, 
then, they occupied certain areas of the North American continent from the Pacific 
to the Atlantic coasts. Judging from their anatomy, their undoubtedly omnivorous 
dental structure, their elongated limbs, and their distribution, it is highly probable 
that these animals were capable of combating adverse conditions when occasion 
required change. While we know that the representatives of this family continued 
in America to a later geological age than was recently believed and that there were 
distinct genera and species during the known existence of the group from the lower 
Oligocene to the middle Miocene, there is yet much to be ascertained and we are far 
from having solved the whole history of this interesting branch of the suborder 
Artiodactyla. When a more extensive survey of Asia, especially its northern part, 
is made, and its Tertiary fauna becomes better known, we probably will be supplied 
with much valuable information on obscure points in connection with the study 
of the vertebrate paleontology of the Tertiary formations of the continents of the 
northern hemisphere. 
