SIWALIK hhinocerotida;. 
39 
unicorn species having been unprovided with lower incisors. The balance of evidence 
therefore seems to he strongly in favour of the view that the form of Siwalik jaw 
without incisors should he referred to B. platyrhinus. This being so, the remaining 
jaw, with two pairs of incisors, must belong to B. palceindicus. 
If the above determinations he correct, the specimens figured in the “Fauna 
Antiqua Sivalensis,” must he redistributed as follows : — 
. R. sivalensis, plate 74, figs. 3, 4. 
R. platyrhinus , „ „ fig. 6 ; pi. 75, fig. 6. 
j U. palceindicus, „ 72, „ 4; „ „ „ 10. 
Mandible of B. sivalensis — Assuming that the mandible, of which a figure, half 
the natural size, is given in plate VI, figure 3 of this volume, belongs to Bhinoceros 
sivalensis , we may proceed to the description of the specimen. It consists of the 
symphysis, and the left horizontal ramus of the mandible, showing the sockets of 
two incisors, and six complete molar teeth. Of the latter, the three last (m. 1. m. 2. 
m. 3) belong to the true molar, and the three earlier to the premolar series ; the latter 
determination being made from the fact that the fourth tooth, counting from the 
left (m. 1), is more worn than the third tooth. The last true molar, though fully pro- 
truded from the alveolus, has not been touched by wear, so that the animal had only 
just attained its full development at the time of its death. The form of the whole jaw 
and teeth is so close to that of the corresponding parts of B. javanieus that it would 
he waste of words to give a detailed description ; and it will, therefore, he sufficient 
to give the measurements of the two specimens. It may, however, he noticed that 
both specimens agree in the absence of the first premolar, which in the living form 
is very generally shed at an early period ; this is in contrast to what occurs in B. in- 
dicus where the first premolar as frequently persists. Apart from the smaller size 
of the recent specimen, the only important difference that can he detected between 
the two is the absence of the alveoli of median incisors in the fossil. This no doubt is 
a very important point of difference, and it is somewhat difficult to account for the 
presence of these teeth in B. javanieus, if, as the other evidence seems to indicate, 
that species he the descendant of B. sivalensis. It is, however, quite possible, as 
already mentioned, that the latter species may have developed median incisors in the 
young state. The following table gives the dimensions of the jaws of the two 
species : — 
R. sivalensis. 
Length of six molars ll'O 
Length of first premolar 1‘3 
Height of „ „ (slightly worn) l’l 
Length of last true molar 21 
Height of „ „ 1'56 
Depth of jaw at first true molar . 3’3 
"Width of narrowest pt. of symphysis 3'4 
Long diameter of incisive alveolus 1‘7 
Shorter „ „ 1*1 
R. javanieus. 
90 
n 
1-0 
1:73 
1*22 
2-4 
2-8 
1-6 
09 
