280 EOCENE AND! MIOCENE FIGS CHAP. 
of dependent processes near the symphysis, which suggest pro- 
cesses occupying a corresponding position in Dinoceras. The 
skull and body are heavy, but the two-toed limbs are slender. 
There is a smaller pair of toes behind these. The dentition 
is complete, and the canines are not inordinately developed. 
The brain is very diminutive. Perhaps #. wintense should be 
separated as a distinct genus, Protelotherium.' — 
Hyotherium (which is regarded as identical with Palaeochoerus) 
has a sharp sagittal crest; the orbit is nearly but not quite 
closed. The canines are not strongly developed. The upper canines 
have double fangs as in 77iconodon among extinct mammals, 
and as in the Hedgehog and other forms among living Mammalia. 
The premolars have the cutting and serrated edge of those of some 
other Pigs, a feature which gives them a curious resemblance to 
the “grinding” teeth of Seals. The molars are tuberculate, and 
like those of living Pigs. It is European and Indian in range, 
and Miocene. 
The genus Choeropotamus has a complete dental formula save 
for the loss of a premolar in the lower jaw. Though it has lost 
this tooth, it is from an older stratum than some of those 
forms which have retained that premolar; it has been found 
in the Upper Eocene of the Isle of Wight and of the neighbour- 
hood of Paris. 
The American and Miocene Chaenohyus has lost the corre- 
sponding teeth of the upper jaw. 
Homacodon* is a genus consisting of several species, which 
has a bunodont and complete dentition. The molars are sex- 
tubercular in the upper jaw. HH. vagans was of about the size 
of a Rabbit, and it appears to have had a curved neck. The 
limbs had five digits, as is so generally the case with Eocene 
Ungulates. It is known from the Middle Eocene of Wyoming. 
Group [IL—RUMINANTIA. 
The Selenodontia or Ruminantia form the second division of 
existing Artiodactyles. The characters of the teeth, which give 
them their name, have already been referred to. . They also 
differ in that there are never more than a single pair of incisors 
1 Osborn, Bull. Amer. Mus. Nat. Hist. vii. 1895, p. 102. 
2 Marsh, Amer. Journ. Sct. xlviii. 1894, p. 262. 
