SIWALIK RHINOCEROTIDA), 
31 
semblance is, therefore, much greater than was at first indicated. Professor Plower 1 
has pointed out how very closely the molars of the two living species resemble 
one another, but has shown that in R. sumatrensis the ‘ posterior valley ’ is re- 
latively deeper than in R. javanicus, and consequently that on the worn masticating 
surface of the former, two 4 fossettes ’ (fossae) exist for a longer time than in the 
latter. In this respect the molars of R. sivalensis agree with those of R. javanicus, 
the ‘posterior valley’ being shallower than the median, and consequently the 
4 posterior fossette ’ disappearing at an earlier period than the median. This is well 
shown in the first true molar of the skull figured in plate LXXIY, figure 5 of the 
44 Eauna Antiqua Sivalensis,” and in two skulls in the Indian Museum. This being 
so, and seeing that R. sumatrensis is further broadly distinguished by its bicorn 
character, and by the relations of the inferior processes of the squamosal, we may con- 
fine ourselves to a comparison with R. javanicus. Between the true molars of these 
two species, taking into consideration the small variation which I have noticed in those 
of the fossil, I am totally unable to discover more than one point in their plan of 
structure which can be taken as affording any certain indication of distinction. 
This point is a difference in the relative dimensions of the molars of the two species. 
Taking little worn teeth, we shall find that in R. sivalensis the greatest length of 
the anterior surface, measuring to the second 4 costa ’ of the 4 buttress,’ is exactly 
equal to the greatest length of the external surface ; whereas in R. javanicus the 
former measurement is greater than the latter. The following measurements show 
this relationship : the two teeth of R. sivalensis, of which the dimensions are given, are 
the specimens figured in this volume (plate Y, fig. 2), and in the preceding volume 
(plate Y, fig. 5) : the measurements of R. javanicus are taken from the teeth of a 
skull in the Indian Museum, and from another in my own possession ; two other 
specimens in the former collection present the same characters : — 
H. sivalensis H. javanicus. 
a. b. a. b. 
Greatest length of outer surface . . . ., . 2 5 2'61 2'0 2'1 
„ „ of anterior „ . . . « 2‘49 2'6 2‘22 2 - 32 
In all the specimens that I can procure this relation appears to be constant. In the 
relation of the transverse to the longitudinal diameter, the teeth of R. sivalensis 
agree with those of R. sumatrensis , but, as already said, differ in other points. Mr. 
Busk pointed out this difference in the relative diameters of the teeth of R. suma- 
trensis and R. javanicus* ; but his conclusions were doubted by Professor Blower. 3 
In such specimens as I have examined the relation is constant. It might be thought 
that size alone would afford sufficient grounds of distinction between the molars of 
R. sivalensis and those of R. javanicus, but although those of the former species 
are in general considerably the large of the two, a specimen described in the sequel 
as a probable variety of R. sivalensis has molar teeth of the same size as those of 
R. javanicus. It will be seen from the above comparisons how very closely the upper 
1 P. Z. S., 1876, p. 449. 2 P. Z. S., 1869, p. 413. 5 Loc. cit. 
