UNGULATA. 343 



Hyotherium. The skull in this genus exhibits a sharp sagittal crest, 

 and the facial region is not bent downwards upon the cranial region. The 

 orbital cavity is nearly separated from the temporal fossa by the close 

 approximation of a postorbital process of the cranium to a similar process 

 from the jugal bone. The dental series is complete, with little or no 

 diastema ; and the canines are premolar-like in shape, while that of the 

 upper jaw is remarkable as exhibiting a cleft root (cf. Triconodon among 

 Mesozoic Mammalia, p. 257). The Upper teeth exhibit a prominent 

 cingulum, and the angular cusps on the molars tend slightly towards 

 the formation of transverse ridges. The hindermost lower molar is 

 produced backwards into a large third lobe bearing one conical cusp. 

 The metapodials presumably referable to this genus, bear a distal keel 

 to work in a corresponding groove of the apposed phalangeal. The 

 typical species, Hyotherium soemmeringi, occurs in the Middle Miocene 

 of Bavaria, Wiirtemberg, Austria, Switzerland, and France ; it must 

 have been about as large as the common wild boar. Other species of 

 the same age are also recorded from the European area, and H. perimense 

 is known by fragments of the dentition from the Siwalik Formation 

 (Lower Pliocene) of Perim Island, in the Gulf of Cambay, Indian 

 Ocean. 



Listriodon. lu another Miocene genus, Listriodon, the cusps of the 

 upper and lower molars fuse into complete transverse ridges, and these 

 teeth hence assume the lophodont form so characteristic of the 'tapirs 

 among Perissodactyla. The skull is shaped like that of a pig ; and 

 the canines, at least in the male, are relatively large, that of the upper 

 jaw being short, thick, and curved upwards, while that of the lower 

 jaw is longer and sharply bent, with its hinder face working upon the 

 opposing tooth. The dental series wants only the first premolar in 

 each jaw. The incisors have short cutting crowns. The premolars are 

 much simpler than the molars ; and all the latter bear two transverse 

 ridges, the hindermost lower molar alone being further complicated by 

 the addition of a small posterior prominence or talon. The typical 

 species is Listriodon splendent, with the skull about 0'36 m. in length, 

 known by various parts of the skeleton from the Middle Miocene of 

 Europe, notably from Sausan and other localities in France, from 

 Switzerland, Germany, Austria, an'd Hungary. Teeth from the Lower 

 Pliocene (Siwalik Formation) of the Punjab, India, have also been referred 

 to this genus (L. pentapotamice). 



Elotherium or Entelodon (fig. 197). The large pig-like animals which 

 became dominant in the Miocene are the most highly specialized of the 

 bunodont artiodactyls, so far as the feet are concerned. The best-known 

 genus is Elotherium or Entelodon, which occurs in the Miocene both of 

 Europe and North America. The basicranial axis of the skull is not bent, 

 but the facial region is remarkably elongated, while the short cranial 

 region rises into a sharp sagittal crest. The orbit is completely separated 



