280 EOCENE AND MIOCENE PIGS CHAP. 



of dependent processes near the symphysis, which suggest pro- 

 cesses occupying a corresponding position in Dinoceras. The 

 skull and body are heavy, but the two-toed limbs are slender. 

 There is a smaller pair of toes behind these. The dentition 

 is complete, and the canines are not inordinately developed. 

 The brain is very diminutive. Perhaps E. uintense should be 

 separated as a distinct genus, Protelotherium. 1 



Hyotherium (which is regarded as identical with Palaeockoerus) 

 has a sharp sagittal crest ; the orbit is nearly but not quite 

 closed. The canines are not strongly developed. The upper canines 

 have double fangs as in Triconodon among extinct mammals, 

 and as in the Hedgehog and other forms among living Mammalia. 

 The premolars have the cutting and serrated edge of those of some 

 other Pigs, a feature which gives them a curious resemblance to 

 the " grinding " teeth of Seals. The molars are tuberculate, and 

 like those of living Pigs. It is European and Indian in range, 

 and Miocene. 



The genus Choeropotamus has a complete dental formula save 

 for the loss of a premolar in the lower jaw. Though it has lost 

 this tooth, it is from an older stratum than some of those 

 forms which have retained that premolar ; it has been found 

 in the Upper Eocene of the Isle of Wight and of the neighbour- 

 hood of Paris. 



The American and Miocene Chaenohyus has lost the corre- 

 sponding teeth of the upper jaw. 



ITomacodon 2 is a genus consisting of several species, which 

 has a bunodont and complete dentition. The molars are sex- 

 tubercular in the upper jaw. H. vagans was of about the size 

 of a Eabbit, and it appears to have had a curved neck. The 

 limbs had five digits, as is so generally the case with Eocene 

 Ungulates. It is known from the Middle Eocene of Wyoming. 



GROUP II. EUMINANTIA. 



The Selenodontia or Euminantia form the second division of 



existing Artiodactyles. The characters of the teeth, which give 



them their name, have already been referred to. They also 



differ in that there are never more than a single pair of incisors 



1 Osborn, Bull. Amer. Mus. Nat. Hist. vii. 1895, p. 102. 



2 Marsh, Amer. Journ. Sci. xlviii. 1894, p. 262. 



