166 Royal Society : — 



ruy own part, though fully convinced that many of the Eocene 

 Hyopotamidce from Mauremont and Egerkingen present, even in 

 their teeth, characters enough to separate them into distinct 

 genera, I shall not do this, as the multiplication of fossil genera, 

 founded solely on dental characters, without adequate knowledge 

 of the skeleton, is more an obstruction than a help to the progress 

 of palaeontology. 



This refers to the Eocene Hyopotamidce of Mauremont and Eger- 

 kingen ; for, having found that among the Eocene members of this 

 family there is one which has lost its lateral digits and acquired a 

 didactyle foot, very like an Anoplotherium, I was obliged to separate 

 this reduced form from its tetradactyle congeners under the name 

 of Diplopus (double foot), while the tetradactyle species of the 

 same family will form the genus Hyopotamus. This diversity 

 among the representatives of the same family is very interesting ; 

 something of the same kind, however, is to be found in our own 

 times in the Hyomoschus, subsisting side by side with the more re- 

 duced ruminants, though this is not an entirely parallel case. More- 

 over, as we have in the Hyopotamidce, so to say, father and son 

 existing together (the complete form together with the reduced), 

 and as, besides, this son bears a great likeness in the typical struc- 

 ture of his limbs to the Anoplotherium, we may infer that the fathers 

 of both reduced forms bore also a general likeness ; and this gives 

 us a clue to the skeletons of the ancestors of the Anoplotheridce, 

 which is still further strengthened by many other considerations, 

 of which I speak more fully in my paper. 



Whilst trying to gain a more complete knowledge of the skeleton 

 of the extinct Paridigitata, I became convinced that we must make 

 some change in our zoological classification of the Ungulata in 

 order to admit the great quantity of genera which have no place 

 in the present system. After the breaking up of the Pachy- 

 dermata (a name that has long enough obstructed science and 

 really checked progress by holding together the most heterogeneous 

 assemblage of animal forms), all the Paridigitata came to be divided 

 into Suina and Ruminantia. This introduction of a physiological 

 function into a system based on the structure of the skeleton is 

 objectionable in the highest degree ; besides, in this classification 

 there is no room for those fossil genera which are certainly not 

 Suina, and most probably did not ruminate. The greater the 

 number of such genera, the better their organization and history are 

 known, the more pressing the necessity to give them some adequate 

 place in our zoological system. As an instance that such a necessity 

 is keenly felt,we may cite Professor Leidy, who, in describing the 

 Oreodontidce, Agriochoeridce, &c. of Nebraska, says that they were 

 " ruminating hogs ;" but in reality they were not hogs at all, and 

 most probably did not ruminate ; what is, then, to be done with 

 them? 



The introduction of Professor Owen's* strict division between 



* Proposed before him by French anatomists, but never carried out completely 



