22 
DE. W. KOWALEVSKY ON THE 
for existence, through geological changes of climate, slow submergence of continents, 
and elevation of the former sea-bottom to the height of the Himalayas, many genera 
must have been destroyed, still some one branch may have remained, and by gradual 
modification through natural selection, and perhaps by the agency of some other un- 
known cause, has given rise to new genera and species better fitted for the changed 
circumstances of life. 
We see the same truth illustrated in the case of the Tapir, which is the last repre- 
sentative of a group extensively developed in the Eocene epoch, as all those genera 
known under the names of Pachynolophus, Lopliiodon , Hyracotherium , Pliolojphus be- 
longed clearly to the family of Tapirince. 
On the contrary, Anojplotherium is exceedingly poor in specific forms, only tw r o being 
known with certainty, without any great difference of size ; and though future discoveries 
may possibly increase the number of species, it is doubtful if ever they were as numerous 
as those of other genera which peopled the earth at the same period. In my opinion, 
as I shall try to prove further on, the Anopl other ium is an aberrant and very reduced 
branch of the early Eocene Paridigitata, which has no direct connexion with the living 
ones, and the true line of descent of our Ruminantia must be traced through other 
genera of the early Eocene epoch. 
If, on the other hand, we turn our attention to the Hyopotamidce , it must be con- 
fessed that the richness of this family in subgeneric and specific forms ranging through 
all sizes is really astonishing ; and we shall be hardly guilty of exaggeration in saying 
that the diversity of Hyopotamidce in the Eocene and Miocene times was as great as the 
wonderful diversity of the Ruminantia is at the present day. That- this is not fully 
acknowledged by palaeontologists is due to the neglect with which this family has been 
treated, and which I shall endeavour to repair. 
Under the name of Ilyopotamidw I understand all the Eocene and Miocene Paridigi- 
tata which had crescentic teeth, with five well-developed lobes on their upper molars. 
The family might be termed Anthracotheridce, as the Anthracotherici are among the 
most prominent representatives of this group ; but the Hyopotcimidce being richer in 
subgeneric forms, the family may perhaps better bear their name. 
The chief character on which the genus Jlyopotamus (under the different names of 
Ancodus, Cyclognathus, Bothriodon ) was founded is the shape of the upper molars, of 
greater breadth than length, and having five well-developed crescents or lobes. No 
author has mentioned any bones belonging to different sets of teeth, on the real or 
supposed differences of which many species were founded. The priority of mentioning 
these teeth under the name of Ancodus is claimed by Pomel in his ‘ Catalogue ; ’ but 
as he neither gave a good description of them, nor illustrated his short notices by figures, 
no palaeontologist has accepted this name, and it may be considered extinct. In fact, 
long before Pomel, Cuvier, having received a jaw of this genus from Puy, compared it 
with Choerojyotamus and An th raco th erium ; and as he had only the back molars, he 
deemed it unnecessary to separate the new animal from Antliracotherium , and designated 
