160 



Dr. W. Kovvalevsky on the 



[Feb. 6, 



existed ; stranger still, it existed in such an ancient period as the close of 

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

 Aym. (Elotherium, Pom., Arcliceotherium, Leidy). The Suilline characters 

 are so striking in this form, that it was at once placed among the Suina, 

 and pronounced tetradactyle, though the confluent tibia and fibula (men- 

 tioned by Leidy) might have been taken as a warning against rash 

 conclusions. I have found in the cabinet of M. Ajnnard, in Puy, some 

 bones of this animal ; few it must be acknowledged, but still leaving no 

 doubt as to the didactyly of Enteloclon. Of this I shall try to adduce more 

 extensive proofs in a forthcoming memoir on this genus. How can the 

 presence of a hog with such reduced limbs be explained in such ancient 

 deposits, when even the living Suiclce have not yet reached this stage of 

 reduction ? The fact, however, is intelligible when we consider that the 

 Enteloclon is the final result of the inadaptive development and reduction 

 along the line of tubercular-toothed Paridigitata ; it is the culmination 

 point of this group, and in this sense quite parallel to the Anoplotliermm in 

 the other group. Thus the Paridigitata, which split dichotomously in the 

 earliest Eocene (?) into two groups, the tubercular-toothed (Bun&clonta) 

 and the crescent-toothed (Selenoclonta), following the inadaptive mode of 

 reduction, reached their culmination point in the Upper Eocene or just 

 above it, in such forms as Enteloclon for the first group, and Anoplotherium, 

 Xiphoclon, Hyopotamus for the second group, which all became extinct 

 without any direct posterity. The living Suina and Ruminantia are not 

 directly connected with them, but are the issue of lateral branches which 

 followed the adaptive mode of development and reduction. 



We may now consider the results of the adaptive mode of reduc- 

 tion. As I said before, the rate of this reduction is much slower in the 

 tubercular-toothed Paridigitata, or Suina ; and this gives us the means of 

 following more closely all the stages of reduction. I propose, there- 

 fore, in the first place, to consider these. 



Though the published materials, as far as the skeleton is concerned, are 

 very poor, we have the means of giving nearly all the intermediate stages 

 between those genera in which the manus and pes are conformable to the 

 true tetradactyle type, every digit (except the fourth and fifth, which are 

 always borne by one) being carried by a separate carpal and tarsal bone, 

 and those in which the entire distal surface of the carpus or tarsus is 

 taken by the enlarged two middle digits. 



The adaptation of these two middle digits on the adaptive line forms a 

 striking contrast to their rigidity exhibited by the other mode of re- 

 duction ; and we shall briefly indicate the stages by which the typical 

 Suilline foot actually passed to reach the stage exhibited now by Dicotyles. 



We are at a total loss to indicate the precise time when the adaptive 

 branch separated from the inadaptive ; it was certainly somewhere in the 

 lowest Miocene, as in the Middle Miocene we find already a large quantity 

 of SuinsB in which the adaptative reduction has fairly set in. As the first 



