161—20 INDIAN TERTIARY AND POST-TERTIARY YERTEBRATA. 
It will be observed from a comparison of the two figures (plate XXIV. figures 
2 and 3) that this tooth is of precisely the same dimensions as the corresponding 
tooth, of the opposite side of the jaw, of Anthracotherium hyopotamoides ; and the 
general resemblance between the two is indeed so close, that, as has already been 
said, they were on a first examination referred to the same species. A closer 
examination has, however, shown that not only must they in all probability be 
referred to distinct species, but according to the present classification to distinct 
genera, though they afford the strongest grounds for the ultimate fusion of these 
two genera. 
It will be simplest to indicate in the first place how the tooth before us differs 
from the upper molar of Anthracotherium hyoyotamoid.es ; and it must be observed 
that this comparison is rendered somewhat difficult by the different states of wear of the 
two specimens. The tooth under Consideration is firstly distinguished from the latter 
by the structure of the enamel, which is marked by longitudinal striae, in place of 
being rugose. 1 It is also distinguished by the presence of a very marked ‘cingulum,’ 
encircling the inner half of the base of the crown. Further, the median transverse 
valley, in place of being of tlie same depth throughout its course, becomes much 
deeper in the middle, and at its outer extremity. Perhaps, however, the most 
important differences occur on the external surfaces of the two teeth ; differences 
unfortunately to a great extent obscured by the fracture of the external angles of 
the specimen under consideration. Those angles, however, when perfect must 
evidently have been greatly produced outwards, and have curved over the flat 
portions of the external surfaces of the two outer columns in much the same manner 
as in typical species of HyopotamusA Again, these surfaces are less nearly vertical, 
sloping more towards the inner side than in A. hyopotamoides , and the centres of 
their bases are depressed below their lateral borders, while all are in one plane in the 
latter. 
The second specimen, which is represented in the 
accompanying woodcut, is also a third left upper molar, as is 
proved by the absence of a pressure disc on the posterior 
side, and is slightly larger than the first specimen. It was also 
obtained in the Bhugti hills, and is in an early stage of wear. 
A part of the anterior side has been broken away, and also 
the enamel of the external surface of the first outer column. 
A comparison of this specimen with the upper molar of 
Anthracotherium hyopotamoides will at once show the striking 
Fig, l. Hmvotwmus JjBK rd differences between the external surfaces of the outer 
left upper true molar.— Bhiigti hiiis. columns of the two specimens, and the greater production of 
the connecting loop in the tooth under consideration. In the second outer column of 
l The difference in th'e structure of the enamel in these two specimens is not shown in the figure, hut is well exhibited in 
the excellent casts in the British Museum. 2 See Owen ‘Quar. Jour. Geol. Soc.,’ Vol. IV., pi. VII. 
