MOLAR TEETH AND OTHER REMAINS OE MAMMALIA. 
37 
new species described above ; the molars of R. iravadicus, however, present a 
tendency towards the hysodont type, and they are characterised by the very open 
median valley, which is a remnant of a primitive type of tooth ; the only true 
brachydont species is A. perimense. As all the Miocene species of European 
Mliinoceros belong to the brachydont type, while the Pliocene species and all exist- 
ing species belong to the hypsodont or specialised type, the Siwalik species of 
Rhinoceros evidently belong to a modern group, and, as far as they go, are another 
argument for the Pliocene age of the deposits in which they occur; while the 
Irawadi species sliows a tendency to an older type, and therefore confirms the con- 
jecture as to the somewhat older date of these Irawadi beds. 
I have lately seen a note in “Nature” (Oct. 1876, p. 572), in which an extract 
is given from a recent paper by Professor Elower (P. Z. S. 1876, p. 443) on the 
crania of Rhinoceros, in which the following interesting difference is pointed out 
between the skulls of the single and double-horned living species ; in the foriner 
group, “ the external auditory meatus is embraced below by the fusion of the post- 
glenoid and post-temporal processes of the squamosal portion of the temporal bone, 
whilst in the other these two processes remain separate.” On looking at the skulls 
of our fossil Indian species, I find that in the crania of R, sivalensis and R. palce- 
indicus — both single-horned species — these two processes are united; on examining 
the cast of Colonel Baker’s cranium of R. platyidiinus (the original of which is in 
the British Museum) — a double-horned species — I find that in this species also the 
two processes are similarly united, the external auditory meatus forming a long 
tubular funnel, looking almost directly upwards, precisely as in the single-horned 
R. indicus {unicornis'). This shows that Professor Flower’s distinction between the 
two groups will not hold for the fossil Indian species ; the union of the two processes 
is another point, in addition to the form of the upper molars, which connects R. platy- 
rhinus with R. indicus, and lends support to the idea that the one may be the 
ancestor of the other. 
Sub-Order: RUMINA.NTIA. 
ViSHNUTHEEiUM IRAVADICUM, nov. gen. nohis, Burma. PI. 7, figs, 1 and 2. 
A short notice of the specimen on which this genus is founded was given by 
me in my paper on the Siwalik fauna {Rec. Oeol. Surv. Ind. vol. IX, pt. 3) ; I now 
give a figure and a more detailed description of the specimen. 
The specimen is a portion of the left ramus of the mandible ; it contains the 
first and second teeth of the permanent molar series ; these have only been in use 
for a short period ; the animal was scarcely adult at the time of its death. The 
inner sides of the anterior barrel of the first molar, and of the posterior barrel 
( 55 ) 
