24 INDIAN TERTIARY AND POST-TERTIARY VERTEBRATA. 
the larger tooth was produced into a £ buttress ’ formed by two similar ridges at the 
antero-external angle, and also carries a fainter 'costa’ opposite the ‘posterior collis. 
In the smaller tooth there appears to be a small ‘ combing-plate ’ projecting from the 
external wall into the ‘median valley ’ and uniting with the ‘ crochet’; while the 
latter extended completely across the valley to join the ‘ anterior collis.’ The union 
of these processes, in the worn condition of the specimen, has resulted in the forma- 
tion of three ‘ fossettes ’ in the ‘ median valley.’ In the larger tooth there is no 
‘ combing-plate,’ and the ‘ crochet ’ does not extend completely across the ‘ median 
valley.’ The ‘ cingulum ’ is only distinctly developed on the anterior surface of 
the teeth, and there is no tubercle at the entrance to the ‘ median valley.’ The 
dimensions of these two teeth are as follows : — 
Length of 2nd milk-molar . . ... . . . 1'8 
Width of „ „ ........ 1'7 
Length of 3rd milk-molar ........ 2'0 
Width of „ „ ........ 2‘15 
The corresponding teeth of the opposite side from Burma, figured and described 
in the first volume, are less worn than the present specimens, and are also of some- 
what smaller size. In all essential characters, however, the two specimens agree 
precisely. The ‘ buttress ’ at the antero-external angle of the third milk-molar from 
Burma appears somewhat less developed than in the corresponding Punjab tooth ; 
this, however, is merely due to the difference in the condition of wear of the two 
specimens. 
Comparisons . — On the assumption that the milk-teeth described above belong 
to Acerotlierium perimense, it will be apparent that they differ from the teeth of 
the permanent series by the much slighter development of the ‘ cingulum,’ and by 
the presence of a ‘combing-plate’ in the second milk-molar. These differences, 
however, should not be taken as affording indications of specific distinctness, as it 
appears to be not unfrecjuently the case that in animals of this family the milk- 
molars differ somewhat from the permanent teeth. Very analogous differences are 
to be observed between the permanent and the milk-molars of the living African 
R. bicornis as figured by De Blainville. 1 In that species the upper true molars show 
a distinct ‘cingulum,’ and either a very small or no ‘combing-plate.’ In the 
milk -molars, on the other hand, there is scarcely any ‘ cingulum,’ and a large 
‘ combing-plate.’ 
Upper incisor. — In figure 4 of plate III a very fine specimen of the unworn 
germ of an upper incisor of a rhinoceros is figured, which must probably be referred 
to the present species. This specimen was discovered by Mr. Theobald in the 
Siwaliks of the Punjab, and has been already referred to, under the name of Rhino- 
ceros planidens in the “Records.” 2 The grounds of assigning this tooth to A. peri- 
mense are, firstly, that it was found in the district where remains of that species are 
of such common occurrence ; secondly, the large size of the tooth itself, which renders 
“ Osteographie ” Atlas, geuus Rhinoceros. 
s Vol. XI, p. 98. 
