120—22 INDIAN TERTIARY AND POST-TERTIARY VERTEBRATA. 
therium may really belong to Bramatherium, though no remains of the latter genus 
have yet been determined from that district. The ‘ costse ’ in the molars of Brama - 
therium seem on the whole to he slightly more pronounced than in ILydaspitheriuni 
megacephalum ' . 
According to Professor Gaudry 1 the upper molars of Helladotherium are very 
like those of Bramatherium, and it is, therefore, probable that if we had only the 
evidence of the teeth to depend on, all the three above-mentioned genera would he 
merged in one. 
Mandible — In cases where more than one species of a genus, or several closely 
allied genera are found in the same formation, there is always extreme difficulty in 
assigning the different remains of these allied forms to their respective owners, and 
this is especially the case in the instance of lower jaws which have to he assigned to 
species named from the skulls or upper jaws and teeth. This difficulty makes itself 
felt in the case of assigning the proper lower jaw to the present species, and the diffi- 
culty is so great that the following determination in the case of this and the next 
species, must be considered to he open to a considerable element of doubt. It has, 
however, been considered preferable to risk wrong association rather than to make 
unnecessary and untrue species upon the evidence of detached lower jaws. In my 
previous notice in the “ Records” so often referred to already, there is briefly de- 
scribed 2 a nearly complete right ramus of the mandible of a sivatheroid ruminant, 
under the name of Hydaspitlierium leptognathus. This jaw was referred to a new 
species, under the impression that the females of the sivatheroids were hornless, 
of which there is now no evidence 3 , and that consequently the one known skull 
of M. megacephalum was that of a full-sized male. The foregoing reference of 
larger upper teeth to the latter species has removed the difficulty of difference of 
size between the skull of H. megacephalum and the present lower jaw, and there 
is, therefore, considerable probability that the latter may be referred to the same 
species. 
The specimen, which was obtained by Mr. Theobald in the Siwaliks of the Pun- 
jab, is represented in plate XIX of this memoir, and will be seen to be nearly com- 
plete, only wanting the sympliysial extremity, and a portion of the coronoid process. 
It is in an excellent state of preservation, and contains the whole of the permanent 
molar series, which has been but a comparatively short time in use, the animal having 
only just attained its full dimensions at the time of its death. 
The general form of the jaw is much like that of the jaw of the giraffe and the 
antelopes, but the horizontal ramus is more curved, both laterally and interiorly, 
than in the former animal, while the anterior border of the ascending portion 
more nearly approximates to a right angle with the long axis of the horizontal 
portion. The ‘angle’ is well developed, but less so than in the giraffe. The 
horizontal portion is slender, and curves outwards to a considerable extent in the 
middle, so that the part immediately below the hinder ‘ crescent ’ of the first 
“ Animaux Fossiles et Gdologie de l’Attique,” p. 260. 2 Vol. XI, pp. 92-93. 3 “ Records,” Vol. XV, p. 31. 
