118 PROCEEDINGS OF THE GEOLOGICAL society. [Noy. 3, 
incisors, as shown in the specimen, figs. 24 & 25, are curved; their 
crown is pointed; the basal line of the enamel is irregular, a piece 
being, as it were, cut out of one side; the concave surface of the 
crown of the tooth presents a median protuberance, and one of its 
borders is crenate: it chiefly differs in being more compressed, so 
that the crown is rather semiconical than conical or cordate. 
From the foregoing details it will be seen that we have now to add 
to the catalogue of extinct British Mammals two quadrupeds, one at 
least as large as the Tapir, the other as the Boar, and, as the lower 
jaw would indicate, with the full complement and kinds of teeth 
characteristic of the typical Ungulata; viz. 
ig ; es : nt Sama ap ee 
3—3° 1-1’ ~ 4—4° 3-3 
The extent of the dental series in the lower jaw of the Hyopotamus 
(Pl. VIII.) is 0°200 (8 inches), or about equal to that of the Tapir 
or the Ass; but though one of the true upper molar teeth surpasses 
in size any of those of the above-cited existing pachyderms, the jaws 
were much more slender and attenuated anteriorly. The extent of 
the contiguous molars and premolars in the lower jaw is 0°115, or 
43+ inches. The presence of what I have described as the typical* or 
‘most complete system of Ungulate dentition} is exemplified in the 
actual creation only in the genus Sus, in which it is not always con- 
stant ; but it appears to have been common in the primeeval forms of 
hoofed animals. Paleotherium, Anoplotherium, Dichobunes, Hip- 
pohyus, Dichodon, Hyracotherium, Anthracotherium, and Hexapro- 
todon were all so endowed, and the same perfect dentition seems to 
have characterized, with certam minor modifications of proportion 
and position, the allied genus Hyopotamus. 
It now remains for consideration in what light we ought to regard, 
with a view to the best interests and steady progress of Palzeontology, 
such minor modifications of the typical dental system. The chief 
characters of the molar and premolar teeth demonstrate that the 
Hyopotamus belonged to the same great natural group of even-toed 
(Artiodactyle) Ungulates as the Hippohyus, Hyracotherium, Dicho- 
don, Cheropotamus, Merycopotamus and Anthracotherium, which 
link together the existing genera Sus and Hippopotamus, and closely 
connect both with the Ruminants. 
In assigning a name to the present interesting addition to this re- 
markable group, I might have followed either the system which 
widens the signification of the generic term, to the extent, e. g. which 
renders Sus equivalent with Phacocherus, Dicotyles, &c., or that 
which restricts it to express the combination of such particular and 
closely-defined characters as are understood by the generic terms Sus, 
Phacocherus, Dicotyles, &c. in most modern systems of mammalogy. 
M. de Blaimville has manifested throughout his great work on 
Osteology a disposition to return to the use of generic terms in the 
wide acceptation which they had in the time of Linneus, or even 
* History of British Fossil Mammalia, p. 433. 
+ Odontography, p. 523. 
= AA. 
