LOPHIODONTIDAZ 373 
general Perissodactyle type, as exemplified in the Rhinoceros and 
the Horse, although on the whole (as might have been expected) 
presenting a closer resemblance to the former. 7. americanus 
differs from 7. indicus by the absence, or at any rate the less 
development, of the intestinal valvule conniventes, the presence 
of a moderator band in the heart, the shape of the glans penis, 
and the more elongated cecum, which is sacculated by four dis- 
tinct longitudinal fibrous bands. The convolutions of the hemi- 
spheres of the brain of the Tapirs are simpler than in other Perisso- 
dactyles, thus tending to confirm the inferences which may be drawn 
from the skeleton and teeth as to the comparatively low or general- 
ised organisation of these animals. 
Palceotapirus—This name has been applied to an imperfectly 
known form from the Upper Eocene Phosphorites of Central France, 
which is regarded by Dr. Filhol as referable to this family. 
Family LOPHIODONTID&. 
Molars brachydont and bilophodont, those of the lower jaw with 
either straight or imperfectly crescentoid ridges ; premolars smaller 
and usually simpler than the molars; last lower molar generally 
with a third lobe. Outer columns of upper molars conical or 
flattened. Digits usually as in the preceding family. 
This family includes a number of more or less imperfectly 
known forms, all of which are extinct and apparently confined to 
the Eocene period, and ranging from the size of a Rabbit to that of 
a Rhinoceros. Although some .of these appear to have died out 
without giving rise to more specialised forms, it is probable that this 
family contained the ancestral types from which most or all of the 
modern Perissodactyles have been derived. Only very brief mention 
can be made here of some of the leading genera. Lophiodon, of the 
Middle and Upper Eocene of Europe, with the dental formula, 
i 3,¢4, p 3, m 3, includes the largest representatives of the family, 
and is generally regarded as a stock which has died out without 
giving rise to later forms. The ridges of the lower molars are 
straight, and the last of these teeth has a third lobe; while the 
second transverse ridge of the last upper premolar is usually incom- 
plete ; the outer columns of the upper molars are flattened, as in 
the next genus. Hyrachyus, of the Upper Eocene of the United 
States, and probably also occurring in the French Eocenes, is an 
allied genus, with four premolars and no third lobe to the last lower 
molar; the fourth upper premolar having the two ridges uniting 
internally to form a crescent. This genus has been regarded as the 
ancestor of the Rhinocerotic Hyracodon. The genus Hyracotherium 
was established in 1839 by Owen for a small animal no larger than 
a Hare, the skull of which was found in the London Clay at Herne 
