ORDER UNGULATA. 



325 



The genus Hyopotamus generally has a more completely seleno- 

 dont dentition than Anthracotherium, but in some species (fig. n 98) 

 these characters are less marked, and thus indicate a complete 

 transition between the two genera. In those species (fig. n 99) 

 which have the most perfectly selenodont dentition the columns of 



Fig. 1 198. — -The third left upper true 

 molar of Hyopotamus giganteus. Up- 

 per Miocene, India. 



Fig. 1199 — The third right 

 upper true molar of Hyopotamus 

 bovinus. Lower Miocene, Isle of 

 Wight. 



the true molars are taller than in the others. The first upper pre- 

 molar is separated by an interval both from the canine and the 

 second premolar. This genus apparently commenced in the Upper 

 Eocene of Europe, and is especially characteristic of the Hempstead 

 beds of the Isle of Wight, and of the Ronzon beds of France, where 

 it is represented by the large H. bovinus (fig. 1199), H. velaunus, 

 and the brachydont H. porcinus. In India it survived till the 

 Upper Miocene, where it is represented by two species, one of 

 which (fig. 1 198) is the largest known form ; it 

 also occurs in the Miocene of North America. 

 The name Diplopus has been applied to 

 a form from the Upper Eocene of Hamp- 

 shire, with only two digits to each foot, which 

 has been referred to this family ; since, how- 

 ever, its dentition is unknown this determina- 

 tion is only provisional, and it has been sug- 

 gested that it may be a Dichodon, although it 

 appears too large for the type species. 



Family Merycopotamid^:. — This family 

 may be regarded as an offshoot from the An- 



thracotheriidce in which the upper true molars (fig. 1200) have only 

 four columns on their crowns ; the dental formula being the same. 

 It is probable that the feet were tetradactylate ; and the mandible 



Fig. 1200. — A right up- 

 per true molar of Meryco- 

 potr.mus dissimilis ; from 

 the Pliocene of India. 



