112 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 3, 
the Anthracotherium magnum. With respect to the lower jaw and 
teeth of the Hyopotamus, their distinctive characters will be best 
brought out by comparing the specimens from the Isle of Wight with 
the beautiful and instructive example of that of the lower jaw and 
teeth of a typical Anthracothere (Anthr. magnum) from Auvergne, 
presented to the Parisian collection by the Abbé Croizet, and which 
is figured of half the natural size in the last published part of the 
‘Ostéographie’ of Prof. de Blainville (G. Anthracotherium, pl. 1. 4. 
D’ Auvergne), and which I have copied, to facilitate the comparison, 
into Pl. VIII. figs.6 & 7. As the fore-part of this jaw and its teeth 
have most suffered, and as the corresponding teeth (incisors, canines, 
and first premolars) are wanting in the fossil jaw about to be com- 
pared (Pl. VIII. figs. 1-4), I shall commence with the last molar 
tooth, which is entire and in place in both specimens, both having 
belonged to adult individuals, with the second or permanent denti- 
tion complete. The last lower molar in Hyopotamus (m 3) is longest 
in the antero-posterior diameter, and supports, as in Anthracothe- 
rium and Cheropotamus, five principal pyramidal lobes, four in two 
transverse pairs, and the fifth single and posterior ; the two transverse 
clefts dividing each pair from the other and from the fifth lobe are 
much deeper in Hyopotamus, and the three primary divisions of the 
crown thus marked off are narrower, higher, and sharper: the trans- 
verse clefts descend obliquely, or smk deeper, in passing from the 
inner to the outer side, where they are closed, as it were, by tuber- 
cular ridges connecting the opposite sides of the bases of the pyra- 
mids ;—but are not continued along the outer side of those bases, as in 
the true Anthracotherium. There is a feeble rismg along the imner 
side of the base of the antero-internal lobe which is continued into 
an angular tubercle at its fore-part, viz.-at the internal and anterior 
angle of the crown, whence a ridge ascends obliquely along the fore- 
part of the crown to the summit of the antero-external lobe ; a paral- 
lel ridge passes from the inner side of the first transverse valley to 
the summit of the second external lobe, and a third parallel ridge 
passes from near the outer end of the second transverse valley to the 
summit of the fifth or posterior lobe: all these three ridges have been 
worn obliquely by the action of the upper grinders. From the middle 
of the two anterior of the oblique ridges a shorter ridge ascends to 
the summit of each of the two internal lobes; and these are con- 
nected with the external lobes by a crescentic ridge passing from sum- 
mit to summit across the back part of the common base of each pair 
of lobes. ‘There is a ridge along the anterior part of the base of the 
crown: but there is no basal ridge upon the back part of the posterior 
lobe, as in the Anthracotherium magnum. A sharp, subcrenate ridge 
extends from the inner end of the second valley to the summit of the 
fifth (posterior) lobe. The inner sides of the two inner lobes are 
broader and less convex than the outer sides of the two outer lobes : 
the opposite shorter sides of each pair of lobes, those viz. that are 
turned towards the middle line of the crown, are nearly flat. In De- 
chodon, which Hyopotamus resembles in the sharp summits and gene- 
ral form of the lobes of the lower molars, more than it does Anthra- 
