84—18 INDIAN TERTIARY AND POST-TERTIARY YERTEBRATA. 
between the inner ‘crescents’ towards these ‘pillars.’ The posterior ‘pillars ’are 
constricted at the point of union with the posterior ‘ crescents ; ’ this constriction, 
however, is only characteristic of an early stage of detrition and disappears at a later 
period, as is shown in the single worn tooth represented in plate XIII, figure 1. 
The enamel is much plicated. 
In figures 1 and 2 of plate XIII are represented two detached upper molar 
teeth of the same species, the first of which (fig. 2 ) is the second right premolar, 
and the other, the third or fourth of the left side of the same series. The former 
tooth is figured to show the characters of the first premolar, and the second to show 
a good example of a well-worn crown of one of the middle teeth. The only point 
that claims any particular notice is that there is a plication of the enamel on the 
inner side of the produced anterior angle of the second premolar, which seems to be 
constant in all specimens of this tooth. 
The dimensions of the three last premolars, and the second and third true mo- 
lars, are as follows : — 
Length of four teeth of specimen drawn in plate XI, fig. 3 4/4 
Length „ second premolar 1'6 
Width „ „ 1-1 
Length „ third 1*24 
Width „ „ 1-12 
Length „ fourth 1'13 
Width „ „ 1-15 
Length „ first true molar l'O 
Width „ „ „ 1-05 
Length „ second „ 1*03 
Width „ „ „ 1-03 
Distinctions and differences . — As I have before observed, it seems doubtful 
whether the evidence of the permanent molars alone would have been sufficient for 
the separation of the present species from the last ; seeing, however, that the milk- 
molars afford undoubted evidence of the distinctness of the two, we may note what 
points of difference can be found between the permanent molars. It will first of 
all be seen from the measurements given above that the permanent molars of H. 
theobaldi are of considerably larger size than those of H. antilopinum ; in the former 
species, moreover, the excess of size of the premolars over the true molars is con- 
siderably greater than in the latter. The anterior ‘pillars’ in the molars of the 
former are more compressed laterally, and stand out more distinctly from the body 
of the teeth than in the latter. These appear to be the main points of difference 
between the permanent molars of the two species. 
The permanent molars of H. gracile seem to be in general somewhat smaller 
than those of II. theobaldi ; while their anterior ‘pillars’ are more cylindrical. 
The projections of enamel from the space between the two inner ‘crescents’ do not 
approach so near to the anterior ‘ pillars ’ in the former as in the latter. In the 
second premolar of the European species the folds of the enamel occurring on the 
inner side of the anterior angle of this tooth in the Indian species are wanting. 
