On the Osteologu of the Hjopotamidie. 



173 



Paridigitata with 

 cresceutic teeth <( 

 .(Selemodonta). 



I said before that earl}'^ iii the Eocene period the group of Pari- 

 digitata spUt dichotomously into two secondary groups, one with 

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

 the Selenodonta, the second Bunodouta (or 8uina). 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- 

 tacarpaha and metatarsaha, five-lobed upper 

 molars, smooth distal extremities of the me- 

 tapodials. Genera : Bothriodon, DicJiobune, 

 Rhaiiatherium, CainotJierium. They reached 

 their highest development and culminated in 

 the didactyle Anoplotheriam, Xiphodon, and 

 Diplopus, which all became extinct without 

 direct successors. 



B. The group following the adap>tlve re- 

 duction separated from the group A some- 

 where in the JMiddle Eocene, by some of the 

 small Uyopotamidm acquiring four-lobed upper 

 molars, as met with at Mauremont, and be- 

 coming Dichodons. Intermediate stages little 

 known ; the Gelacus is one of them. The 

 least-reduced h^ing form is Hyomosclins. Cul- 

 minating in recent times in the didactyle Bo- 

 vidce and Antilopidce. 



A. Group follo\\dng the inadaptive reduc- 

 tion very little known. Acotherulum and an- 

 other larger hog-like animal from the JMiddle 

 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 Chosrothc- 

 rium from San sans, with the phalangeal ridge 

 not yet extending over the whole distal end of 

 the metapodium. Palc&ochwrus : reduction has 

 fairly set in on the adaptive mode, the pha- 

 langeal ridge passing over the whole end of 

 metapodial, ^ns still more reduced. Dico- 

 ti/les : all the distal surface of the carpus and 

 tarsus taken by the enlarged middle digits, 

 i^ Tending to become didactyle. 



We must briefly consider each of these groups. 



The Paridigitata with crosceutic teeth follo\\-ing (he inadaptive 



Paridigitata with 

 tubercular teeth 

 (Bunodonta or 

 Suina). 



