LOPHIODONTID& 3 73 



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. T. americanus 

 differs from T. indicus by the absence, or at any rate the less 

 development, of the intestinal valvulae conniventes, the presence 

 of a moderator band in the heart, the shape of the glans penis, 

 and the more elongated caecum, 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. 



Palceotapims. 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, 

 * f > c T> P f > m f > 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 



