SIWALIK EHINOCELlOTIDiE. 17 
large and triangular in shape : the postero-external angle of the tooth is produced 
into a wedge-shaped process. 
Identity with 11. planidens . — If this tooth he compared with the two fragmen- 
tary upper molars, drawn in figures 7 and 9 of plate IV of the first volume of this 
work, and upon the evidence of which the new species I. planidens was founded, 
it will he at once apparent that all three teeth belong to the same species. 
2nd true molar. — The second true molar in the figured upper dentition is un- 
fortunately so much broken that only its anterior half remains. This portion shows 
that the tooth had a large antero-external c buttress,’ and that the ‘ cingulum ’ was 
interrupted on the inner surfaces of the two * colies. ’ There is a large c crochet,’ 
and the rudiment of a c combing-plate,’ which, however, does not extend to the base 
of the e median valley.’ As this tooth is so imperfect, another and complete speci- 
men* also obtained by Mr. Theobald from the Siwaliks of the Punjab, has been 
drawn in figure 3 of plate III. 1 This tooth agrees very closely in general characters 
with the second true molar in the previous plate, and is evidently the corresponding 
tooth of the opposite (right) side of the jaw of the same species. The isolated tooth, 
however, differs slightly in the form of the c cingulum ’ from the corresponding tooth 
in the full series. This difference consists in the fact of the ‘ cingulum ’ being 
less distinctly crenulated and more closely applied to the surface of the crown, and 
also that it forms a continuous, although a thin, fine along the internal surface of 
the ‘ anterior collis.’ In respect of the form of the ‘ median valley,’ e crochet,’ and 
‘ colies,’ the two teeth are identical. 
Identity with R. iravadicus. — If the figure of the above-described second upper 
true molar of A.cerotherium perimense (pi. III., fig. 3) he compared with the corre- 
sponding tooth of a rhinoceros from Burma, drawn in plate V, fig. 2 of the first 
volume of this work under the name of R. iravadicus, it will he found that in 
general characters the two teeth are absolutely alike, and they must consequently he 
referred to the same species. As the last mentioned tooth, together with a corre- 
sponding tooth of the opposite side (vol. I., pi. V., fig. 1) were the types on which the 
species R. iravadicus was established, it is evident that this species must he merged 
in Acerotherium perimense. It was impossible, from the materials at hand at the 
time of publication of the second part of the first volume, to identify the teeth 
described under the name of R. iravadicus, either with those described as R. plani- 
dens, or with those as A. perimense. It has been shown that there is a certain 
amount of variability in the upper molar teeth of A. perimense, and it required a 
large series of specimens to demonstrate the unity of species of these several varieties. 
In figure 3 of plate V. of the first volume an imperfect occiput of a rhinoceros from 
Burma, was also figured under the name of R. iravadicus. As far as can he judged 
from this specimen, it appears to agree very closely in form with the cranium of 
A . perimense described above, and may, therefore, probably be referred to that species. 
1 The specimen was lithographed in my absence, and has unfortunately been placed somewhat out of its proper 
position. 
