OSTEOLOGY OF THE H Y OPOT AMULE. 
23 
it under the name of Anthracotherium velaunum. In the year 1847, however, Professor 
Owen, having received from the Marchioness of Hastings very good materials, as far as 
the dentition was concerned, studied with great accuracy the structure of these teeth, 
and found in them sufficient characteristic differences to justify their separation from 
Anthracotherium under the name of Ilyopotamus. Notwithstanding that one of the 
characters on which the distinction was based (the complexity of the upper premolars) 
w ? as found to be a mistake, these complex teeth being milk-molars and not premolars 
of the permanent dentition (see Quart. Journ. Geol. Soc. vol. iv. 1848, pi. vii. fig. 6 ; p 3 
and p 3 are in reality rZ 4 and cl 3 ), still there were other characters which entirely justified 
the distinction, as I shall show when we arrive at the description of the teeth. Pro- 
fessor Owen gave such a thoroughly good and accurate description of these teeth, 
accompanied with plates, that he may be considered the founder of the genus. One 
year later, M. Aymard, of Puy, in a footnote to his paper on Entelodon , mentioned the 
Hyopotamidce from Ronzon (Puy) under the name of Bothriodon , as he believed them 
different from those described by Professor Owen from Hempstead. But having com- 
pared an extensive series of jaws and parts of skulls from both localities, I have been 
unable to detect any difference in them, and therefore the fossils from Puy must be 
included under the same generic name as those from Hempstead. The only author 
who has accepted the genus Bothriodon of Aymard is Professor Gervais, who, in his 
‘ Paleontologie Franchise, ’ p. 192, says that the Ilyopotamus is to be distinguished 
from Bothriodon ; but I have not been able to find any reasons adduced in the de- 
scriptions of the two genera why Professor Gervais considers them distinct, or on what 
characters he has founded his distinction. Notwithstanding the care with which I insti- 
tuted my comparison, I could not detect any differences between the Hyopotamidce from 
Puy and those from Hempstead ; and, so far as I can see, their separation into two 
distinct genera is entirely unfounded. Professor Gervais has described many portions of 
jaws from different localities in France, and has given them different specific names, the 
distinction being founded on size and on the fact of their having been found in different 
localities. As I reserve the discussion of specific differences for the end of my paper, 
I will not enter into the criticism of these doubtful species just now. 
In the year 1861, Professor Rutimeyer figured and described, with great accuracy, 
some few upper molars of a small Hyopotamoid animal from Egerkingen. These teeth 
had, however, been previously referred by H. v. Meyer to a (new genus, Tapinodon. 
Professor Rutimeyer had only true molar teeth from Egerkingen, and as they really did 
not present any fundamental difference from the Hyopotami of Professor Owen, he 
considered them to belong to the same genus. The Egerkingen specimens being very 
small, Rutimeyer separated them specifically under the name of Hyopotamus Gresslyi. 
This discovery was very important, as it carried the genus into undoubted and even early 
Eocene strata*. Then came the discovery of the wonderfully rich Eocene fauna of 
* I have no doubt that the small Eocene Hyopotamidce will one day be generically separated from the true 
Hyopotami, as known from Puy and Hempstead, as their premolars are somewhat different. I shall not do 
