ORDER UNGULATA. 1 32 1 



Pliocene of Algeria and India. Remains of Phacochoerus occur in 

 superficial deposits in Africa. The last molar of this genus com- 

 pared with that of Hyotherium presents a difference analogous to 

 that between the corresponding teeth of Mastodon and the Mam- 

 moth. 



We may now revert to the consideration of more generalised 

 types. The most important is Hyotherium (in which may be included 

 Palceochozrus and Chai-omorus) which presents characters connect- 

 ing it with Dicotyks, Sus, and Choeropotamus, and may have been 

 the ancestor of the first 

 two of these genera. The 

 upper true molars (fig. 

 1 195) have low, square 

 crowns, with a rudimentary 

 fifth column, which is fully 

 developed in Choeropota- 

 mus ; and the last true 

 molar comes into use be- 

 fore the first is worn. In m. 1. 

 the third upper true molar Fig< II95 ._ The left upper true molars of Hyothe . 



there is no third lobe, and rium perimense ; from the Pliocene of India. 



this lobe is small in the 



corresponding lower tooth ; while occasionally the last upper pre- 

 molar has only a single outer column, as in Choeropotamus. The 

 canines are scarcely larger than the incisors ; are oval in section, 

 and the lower one is not received into a notch in the upper jaw. 

 The lateral metapodials are stouter than in modern pigs. In Europe 

 this genus ranges from the Quercy Phosphorites to the Middle 

 Miocene of the Continent ; while in India it occurs in the Lower 

 Siwaliks of Sind, and also in Perim Island (fig. 1 195) ; the American 

 forms which have been referred to this genus are regarded by Pro- 

 fessor Cope as distinct. Hippohyus, of the Indian Siwaliks, appears 

 to be an allied but specialised form, in which the crowns of the 

 molars are much taller, and have lateral infoldings of the enamel, 

 whereby an extremely complex pattern is produced on their worn 

 surfaces. Sa?iitherium of the Siwaliks must be placed with this 

 group ; while Doliochcerus of the Quercy Phosphorites is apparently 

 allied to Hyotherium, although it may also have affinity with Cebo- 

 chcerus. The genus Babirusa, of Celebes, is unknown in a fossil 

 state. 



In the John Day Miocene of the United States there occur pig- 

 like animals apparently connecting Hyotherium with the existing 

 Peccaries, most of which may be included in the genus Chcenohyus. 

 These forms agree with Hyotherium in having the fourth upper pre- 

 molar simpler than the true molars, but have the lower canine with 



