. An introduction to the study of mammals living and extinct. Mammals. 374 UNGULATA Bay. A more nearly perfect specimen, apparently of the same species, was afterwards (in 1857) described under the name of PUolophus vulpi- ceps, of which the skull is figured in the accompanying woodcut. Other forms referable to the same genus have been obtained from the Wasatch Eocene of the United States, and were described by Professor Marsh under the name of Eohippus. There were four premolars, the fourth being unlike the molars, and in the upper jaw having only one inner cusp. The upper molars are of the g
. An introduction to the study of mammals living and extinct. Mammals. 374 UNGULATA Bay. A more nearly perfect specimen, apparently of the same species, was afterwards (in 1857) described under the name of PUolophus vulpi- ceps, of which the skull is figured in the accompanying woodcut. Other forms referable to the same genus have been obtained from the Wasatch Eocene of the United States, and were described by Professor Marsh under the name of Eohippus. There were four premolars, the fourth being unlike the molars, and in the upper jaw having only one inner cusp. The upper molars are of the general type of those of Lophiodon, but have conical outer columns, and the anterior transverse ridge imperfect, while the ridges of the lower molars are crescentoid. Systemodon differs from Hyracotherium. Fig. 163.âEight side of skull of Hyracotherlnum leporinum, from the London Clay, i natural size. (After Owen.) 3, Occiput; f, sagittal crest; 11, frontals ; 15, nasals ; 21, maxilla; 22, premaxilla; d, mandibular condyle ; a, aperture of facial nerve; p 1-4, premolars ; m 1-3, molars! by the absence of a diastema between the first and second pre- molars; it occurs in the Wasatch Lower Eocene of the United States. In Pachynolophus (Lophiotherium, Orotherium, or Orohippus), which is common to the Middle and Upper Eocene of Europe and the Bridger Eocene of North America, the outer columns of the upper molars are flattened, and in some cases, at least, the last premolar resembles the molars, that of the upper jaw having two inner cusps.^ This genus, indeed, so closely connects Hyracotherium with the genera Epihippus^ and Jnchilophus as to show that the distinction between the LopUodontidcn and Fakeotheriidce is really an arbitrary one. EpiUppus, of the Upper Eocene of the United States, has both the third and fourth upper premolars as complex in the molars, and is distinguished from Anchilophns by the lower cusps and more imperfect transverse ridges of these teeth. The so-called
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