1 76 livijal Socieli/ : — 



libriuin. Now the couflueuce of the two middle digits is always 

 followed by a considerable contraction ; and if this coalescence 

 should occur in the imperfectly adapted foot of Amplotherium, and 

 especially Xiphodon, all equilibrium would be lost. If ever such 

 confluence occurred, by reason of the tendency to the greatest pos- 

 sible reduction, the resulting form had not the least chance of being 

 propagated and of holding its ground against the competing genera. 

 The broadening of the middle digits could not occur after the entire 

 loss of the laterals ; and we shall see that, in genera which have left 

 immediate successors {tim, Hyomoscluus), the lateral digits are not 

 allowed to go until the middle ones have obtained a secure footing 

 on the entire distal surface of the carpus and tarsus. However, 

 these iiiadaptively reduced genera of the Eocene could perhaps have 

 lived till our ov\-n days ; but the development of the competing and 

 better adapted forms pressing them on all sides, they had no chance 

 to stand their ground against them, and became extinct without 

 any direct posterity, while the succession of the Paridigitata ISele- 

 nodouta was carried by a side branch, and reached its culminating 

 point in the Miocene, continuing from then to our own days. 



We turn now to the same mode of inadaptive reduction as mani- 

 fested by the tubercular-toothed Paridigitata (Bunodonta), or Suina. 

 The old representatives of this group are very little knovMi. The 

 Clweropjotamm is a very doubtful genus, and may be inclining towards 

 the crescentic-toothed Paridigitata, beiug supposed to be the pro- 

 genitor of the AntJiracotheridce and Hyopotamidce. Besides it we have 

 the Acotherulum satarninwn, Ger., a tridy tubercular-toothed Paridi- 

 gitate from the Upper Eocene, Acothendum Campidiii (Dicliohune 

 Camp., Pictet) from the Lower Eocene of Mauremont, and a larger 

 pig-like animal from the same deposit not yet described or named. 

 These are undoubtedly the oldest tubercular-toothed Paridigitates 

 \^'e know ; but unfortunately our knowledge is based only on dental 

 characters. However, considering that even the recent ISuina have 

 not yet completely lost their two lateral digits, it may, ^^"ith the 

 greatest probability, be inferred that these old Eocene forms were 

 tetradactyle. Our knowledge of the development of this group is 

 very incomplete ; but there can be no doubt that, though not nearly 

 so rich as the Seleuodont group, they were still numerous, as may 

 be inferred from the great quantity of the Suina in the Miocene, 

 and such forms as the Listriodon splendens *. We are so accus- 

 tomed to loolf on the 8uina as a group of tubercular-toothed tetra- 

 dccctyle Paridigitata, that no one ever thought of the possibility of a 

 didactyle hog ; but, strange as it may seem, such a Suilline animal 

 existed ; stranger stUl, it existed in such an ancient period as the 

 close of the Eocene in the lowest strata of Eonzon at Puy. This is 

 the Entelodon, Aym. (Elotherium, Pom., Archceotherium, Leidy). 

 The Siulline characters are so striking in this form, that it was at 



* I have not been so fortunate as to see any bones of the Listriodon ; but 

 as this raiocene hog died without any successors, I should not be astonished if 

 it prove to be didactyle, thus being a parallel to Hi/ojpotamvs in the same 

 sense as Lntdodon is parallel to Anoploihcrium. 



