On the Osteology of the Hyopotamidse. 165 



not a single paper in which the osteology of an extinct genus 

 of Paridigitata has been fully given *. This may partly be the 

 reason that the pedigree of living genera has hitherto been so 

 obscure. 



The Paridigitata of the Paris gypsum, described in a masterly 

 way by Cuvier (the Anoplotherium and Xiphodon), were clearly ex- 

 tremely reduced descendants of some earlier more complete forms ; 

 their feet presented, in fact, nearly the same degree of reduction 

 which we find in our recent Ruininantia, save the confluence in a 

 cannonbone. Seeing the reduced state of their skeleton, how could 

 they be taken as progenitors of the very rich family of Ruminants, 

 some of which have retained, even till our times, a tetradactyle 

 limb ? However, so great was the want of some form from which 

 the living Ruininantia could be assumed to be derived, that nearly 

 all comparative anatomists and palaeontologists who speculated on 

 these questions of descent, placed the Anoplotherium and Xiphodon 

 at the head of the series, as the fons et origo wherefrom all living 

 Ruininantia have descended. 



The present paper is an attempt to introduce to palaeontologists 

 a new form, which, though kuown by its dental system more than 

 twenty-five years ago, has remained totally unknown, so far as 

 its skeleton is concerned. This skeleton, by its completeness, has 

 proved to be a very interesting one, not only in a concrete way, 

 but as furnishing a clue to the understanding of the skeletons of 

 those forms which, though totally unknown, must have preceded 

 Anoplotherium and Xiphodon in time, and from which these two may 

 have descended. 



Besides, the greater importance of the Hyopotamidce in comparison 

 with Anoplotherium and Xiphodon lies in the fact, that, while these 

 two last were but poorly differentiated, presenting only two or three 

 distinct specific forms, the Hyopotamidce, on the contrary, strike 

 us by the extreme diversity and richness of their specific and generic 

 forms. Beginning in the Middle or Lower Eocene of Mauremont, 

 they existed until the Lower Miocene period ; and, judging by the 

 great number of species and genera, they must have filled in the 

 fauna of this period the same important place which the greatly 

 diversified Ruminantia fill in the fauna of our own times. Indeed 

 the differentiation of Hyopotamidce may be said to be even greater, 

 in point of size, as they range from the Hyopotamus Renevieri, not 

 larger than a rabbit, to the great Anthracoiherium of Rochette, 

 which is as big as our Hippopotamus — all the intermediate stages 

 between these two extremes being represented by different genera, 

 subgenera, and species of the same family. 



I hope that the rich development of this much neglected family 

 will arouse the attention of palaeontologists, and that the skeletons 

 of the different members will be more thoroughly investigated. Por 



* No doubt we have excellent memoirs, like the works of Gaudry, Kiitimeyer, 

 Fraas, and H. v. Meyer; but the Paridigitata described in all these do not 

 materially differ from those now living, at least so far as the skeleton is con- 

 cerned. 



