On the Osteology of the Hyopotamiclje. 



173 



I said before that early in the Eocene period the group of Pari- 

 digitata split dichotoruously into two secondary groups, one with 

 crescentic teeth, the other with tubercular ; the first I have called 

 the Selenodonta, the second Bunodonta (or Suina). Now each of 

 these secondary groups followed a twofold mode of descent, one of 

 which I term the inadaptive, and the other the adaptive, thus, finally, 

 giving rise to four distinct groups : — 



A. The group following the inadaptive re- 

 ductions develope enormously in Eocene and 

 Middle Miocene times : all have distinct me- 

 tacarpalia and metatarsalia, five-lobed upper 

 molars, smooth distal extremities of the me- 

 tapodials. Genera : Bothriodon, Dichobune, 

 Bhagatherium, CainotJierium. They reached 

 their highest development and culminated in 

 the didactyle Anoplotlierimn, Xiphodon, and 



Paridigitata with Diplopus, which all became extinct without 



crescentic teeth \ direct successors. 



(Selenodonta). B. The group following the adaptive re- 



duction separated from the group A some- 

 where in the Middle Eocene, by some of the 

 small Hyopotamidce acquiring four-lobed upper 

 molars, as met with at Mauremont, and be- 

 coming Diclwdons. Intermediate stages little 

 known; the Gelacus is one of them. The 

 least-reduced living form is Hyomoschus. Cul- 

 minating in recent times in the didactyle Bo- 

 \vida; and Antilopidce. 



j A. Group following the inadaptive reduc- 

 tion very little known. Acoiherulvm and an- 

 other larger hog-like animal from the Middle 

 and Upper Eocene may belong to this group ; 

 they were certainly tetradactyle. Culminated 

 in the lowest Miocene in the didactyle Ente- 

 lodon: no successors. 



B. Group following the adaptive reduction, 

 branched from the group A in the Eocene ; the 



^ most typical representative is the Choerothe- 

 rium from Sansans, with the phalangeal ridge 

 not yet extending over the whole distal end of 

 the metapodium. Palwochcerus : reduction has 

 fairly set in on the adaptive mode, the pha- 

 langeal ridge passing over the whole end of 

 metapodial. Sm still more reduced. Dico- 

 tyles : all the distal surface of the carpus and 

 tarsus taken by the enlarged middle digits. 

 (_ Tending to become didactyle. 



We must briefly consider each of these groups. 



The Paridigitata with crescentic teeth following the inadaptive 



Paridigitata with 

 tubercular teeth 

 (Bunodonta or 

 tSuina). 



