ORDER UNGULATA. 



355 



generally has a third lobe ; and there are usually four digits in the 

 manus and three in the pes. The type genus Lophiodon (fig. 

 1228, a) comprises some species which attain a bulk rivalling that of 



X I 7. 7. 



the Rhinoceroses, and has the dental formula I. -, C. — , Pm. -, M. -. 



3i 3 3 



It is found in the Middle and Upper Eocene of Europe, and is 

 generally regarded as having died out without descendants. In 

 the dentition here figured the inner crescent of the fourth upper 

 premolar is incomplete, and the ridges of the lower molars are 

 simple ; the last lower true molar always has a third lobe. Allied 

 to Lophiodon is Helaletes (Desmatotherium), of the Upper Eocene 

 of North America, characterised by the more rounded upper true 

 molars and the absence of a diastema in the lower jaw ; it is re- 



Fig. 1228. — a, The last five right upper cheek-teeth of Lophiodon isselensis, from the Middle 

 Eocene of France ; b, The right upper cheek-teeth of Hyrachyus agrarius, from the Eocene of 

 North America. Reduced. 



garded by Professor Cope as an ancestral stock of the Rhinocerotidce . 

 With forms from the North American Eocene described as Isectolo- 

 phus and Prothyracodon, in the first of which the last lower true 

 molar has a third lobe, we come to the consideration of Lophio- 

 donts showing more affinity with the Tapirs, but it does not appear 

 quite certain that both these forms are really entitled to generic dis- 

 tinction from the next. The genus Hyrachyus (fig. 1228, b), which 

 occurs typically in the Uinta and Bridger Eocene of the United 

 States, is taken by Dr Filhol to include European Lophiodonts 

 ranging from the Middle Eocene of France to the Lower Miocene 

 of St Gerand-le-Puy. This genus has four premolars, of which the 

 last is somewhat simpler than the first true molar ; while there is 

 no third lobe to the last lower true molar. In the type species the 



