MOLAR TEETH AND OTHER REMAINS OE MAMMALIA. 
35 
also be remembered that many of the latter are distinguished simply on external 
characters — a kind of evidence not available in the case of fossil species. 
Of three of the above fossil species, viz., R. sivalensis, R. palceindicus, and 
R. platyrhinus, the crania, in a more or less complete state, have been discovered. 
The two first species were unicorn and the latter bicorn. The fossil forms do not 
bear out the relationship between the number of horns and the lower incisors 
which occur in the living species, and which Dr. Gray has taken as a character 
affording a distinction of sub-generic value. Among the living species, in the 
single-horned forms, the mandible has one pair of large outer incisors, and a smaller 
median pair; while the two-horned forms have only the outer pair of incisors 
present. Precisely the reverse of the above occurs among the Sivalik species : 
the bicorn R. platyrlimus has a pair of large outer incisors in the mandible, and 
a smaller central pair; while the unicorn R. palcemdicus has the outer pair only. 
{See Fauna Antiqua Sivalensis,’^ Rlate 74, Fig. 4, and Rlate 75, Fig. 10.) Dr. 
Gray’s distinction, therefore, founded, on this relationship, is not of real classifica- 
tory value, as it is confined to the species of Rhinoceros of one period only. 
A statement made on the authority of Dr. Ealconer regarding Siwalik Mam- 
mals, must of course meet with general acceptance ; in relation, however, to our 
present subject, there is one which does not appear to me to be borne out by the 
facts at our command. In the “ Introduction to the Siwalik Eauna” (Ealconer’s 
“ Ralceontological Memoirs^’ Vol. I, p. 21), it is stated that Rhinoceros sivalensis 
was provided with six incisors in both the upper and lower jaws ; that this 
statement was not a local error we infer from a passage in Owen’s “Odontography,” 
{Vol. I, p. 589), where it is asserted, from the verbal authority of Dr. Ealconer, that 
one of the Siwalik Rhinocerotes was “ hexaprotodont” in both jaws ; this species 
can only be Rhinoceros sivalensis. None of the figures, however, in the “ Eauna 
Antiqua Sivalensis ” bear out this statement, as none of the incisor teeth of 
R. sivalensis are shown : a figure of the mandible of this species, however {plate 
75, Fig. 6), shows the whole of the molar and premolar series, but no incisors. In 
this figure, the anterior premolars extend almost up to the symphysis of the mandi- 
ble, precisely in the same manner as in the mandibles of Rhinoceros leptorhinus 
of Cuvier {Owen, British Fossil Mammals, Fig. 135), and of the African Rhinoceros 
simus {De Blainville’s Osteographie, Vol. Ill, Rhinoceros, Rlate 4), in both of which 
species there are no persistent incisors. In all recent Rhinocerotes, in which the lower 
incisors are persistent, the symphysis of the mandible is prolonged in a spatulate form, 
considerably in advance of the first premolar, and there is a very long diastema 
between the two series of teeth {Owen’s “ Odontography,” Vol. I, p. 596). In 
the mandible of Rhinoceros sivalensis there seems to be no room for six incisors, 
even without a diastema, a condition quite unknown in any animals of this class. 
It appears to me that until some conclusive evidence of the hexaprotodont charac- 
ter of this species be forthcoming, we are quite justified in regarding it as being 
without permanent incisors. It is, to say the least, very remarkable that if 
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