SIWALIK RHINOCEROTIim 
57 
ingly been provisionally identified ; it fs, however, very nrucli to be desired that 
the cranium of the Narbada form may some day be obtained in order to see 
whether there may be any difference between it and the living form. Of the 
rhinoceroses of the pliocene (Siwalik), no form can be decidly fixed upon as the 
direct ancestor of R. indicus } The Siwalik R. palceindicus, however, if all the 
remains assigned to it above be correctly referred, agrees with the large living Indian 
species in being unicorn, and also in the form of the mandible and the number of 
its lower incisors. In the form of its upper true molars this species, moreover, makes 
an approach to the living species, since its teeth lack the distinct ‘ buttress 5 at the 
antero-external angle, so characteristic of the teeth of the Sumatran type. There is 
no £ combing-plate ’ in the true-molars of JR. palceindicus, the presence of which is such 
a characteristic feature in those of R. indicus : the want of this process in the earlier 
form might, however, be readily explained by evolution, as it never occurs in molars 
of the Sumatran type, to which those of all the species of Acer other ium belong. 
In the above respects the upper molars of R. palceindicus are exactly intermediate 
in character between those of the Sumatran or Acerotherian type, and those of 
R. indicus, and it has accordingly appeared to me not improbable that R. palceindicus 
may belong to the stirps from which the living species has been derived, though the 
line of descent may not have been directly through the former. 
We now come to the consideration of the living bicorn Indian species 
R. sumatrensis, which with R. lasiotis" is the modern representative of the group 
Ceratorliinus. Professor Flower has shown in what respects the European miocene 
R. scleiermacheri, which belongs to the same group, resembles and differs from the 
living species. The latter is distinguished from the former by the non-union of the 
post-glenoid and post-tympanic processes of the squamosal below the meatus 
auditorius ; it is also further distinguished by the presence of one, in place of two 
pairs, of incisors in both upper and lower jaws. As is observed by Professor Elower , 3 
the difference in the number of the teeth of the two forms is in accordance with 
the hypothesis of the evolution of the one from the other, being a progress from the 
general to the special. The relations of the squamosal processes point, however, 
exactly in the opposite direction, being from the special to the general, and it is ac- 
cordingly very hard to see how the miocene can be the direct ancestor of the recent 
species. The general form of the skulls and mandibles of the two forms, as is noticed 
by Professor Gaudry , 4 is, however, so very similar that it seems probable they are 
closely related. Both species may have been derived from a common stock, from 
which R. scleiermacheri branched off at an earlier period, the direct progenitor of 
R. sumatrensis being, according to this view, still unknown. 
1 On page 55 of the first volume of this work it was suggested, perhaps somewhat hastily, that B. indicus was 
descended from B. platyrhinus : the re-determination of the mandible of the latter, apart from the horn-question 
shows that this idea cannot be entertained. 
2 B. lasiotis, if it be more than a variety of B. sumatrensis, is not distinguished, as far as is known, by any 
peculiar dental or osteological characters. 
3 Loc. cit., page 456. 4 Loc. cit., pp. 44-45. 
