SIWALIK RHINOCEROTIDiE. 
41 
not improbable that tlie Gaj skull is not fully developed in this respect. Again, the 
hinder portion of a small skull of a fossil rhinoceros from the Siwaliks, figured by 
Messrs. Baker and Durand, 1 agrees with the Gaj specimen in size and form. This 
skull was considered by those writers as belonging to a young individual of R. siva- 
l&nsis ; and if this determination be correct, it would show that the Gaj specimen is 
probably a young individual of the same. On the whole, it seems to me probable that 
the Gaj skull would never have developed such a high occipital region as the typical 
skulls of R. sivalensis ; but, as we shall see below, there is such an intimate con- 
nection between the upper molars of the two forms that there would be great diffi- 
culty in making any well-defined specific distinctions, although, as already said, 
there is a possibility of the specific distinctness of one form. The Gdj skull exhibits 
very clearly the union of the post- glenoid and post- tympanic processes of the squa- 
mosal below the auditory meatus, a character which it shares, as far as is known, 
with all unicorn members of the family. 
Upper true molar . — The upper molar drawn in figure 7 of plate V is the one 
nearly perfect specimen found with the Sind skull ; it has unfortunately been 
broken on the free edge of the outer wall : when perfect it could only have been 
just touched by wear on this outer side, as the summits of the two c colles ’ are still 
intact. The antero-posterior elongation of this tooth shows that it cannot belong 
to the premolar series ; while the great development of the c buttress ’ at the antero- 
external angle, and the curvature of the external, or dorsal surface, equally shows 
that it cannot be a milk-molar. The specimen must, therefore, be either the first or 
the second true molar. If the figure of this tooth be compared with that of the 
second upper true molar of R. sivalensis drawn in figure 2 of the same plate, it will 
be seen that, except as regards size, the two are exceedingly alike. The only 
differences that I can detect are that in the smaller tooth the groove on the posterior 
aspect of the 4 anterior collis 5 is more pronounced, and the ensuing accessory spur 
considerably more developed than in the larger specimen ; in the former there is also 
a distinct tubercle at the entrance to the 4 median valley,’ of which only a trace 
exists in the larger. Both agree in the form of the 4 posterior valley.’ In the teeth 
which are here provisionally considered as the milk-molars of R. sivalensis, there is 
the same conformation of the 4 anterior collis ’ as in the Gaj specimen ; consequently, 
since ancestral characters are often retained in the milk-molars, and if all the teeth 
belong to the same species, it would seem that in the Gaj race the form of the 
4 anterior collis ’ was the most complex ; in the higher Manchhar form it was slightly 
less so, and in the highest Siwalik form it had become quite simple, its original 
complexity being retained only in the milk-molars. 
Seeing thus that a transition can be traced from the Gaj molar, through the 
Manchhar, to the Siwalik specimen, there appear to be no valid grounds for 
assigning the first to a distinct species ; as, however, the Gaj form is of consider 
ably smaller size than either of the others, and as it presents certain points of 
1 Loc. cit., pi. XVII, fig. 9. 
