SIWALIK RHINOCEROTIDiE. 
21 
A. jemezanm , 1 was described upon the evidence of the mandible only, and I do not 
know whether the upper molars have been subsequently discovered. In A. mala- 
corhinus 2 the 4 cingulum ’ extends continuously round the whole of the inner 
surface of all the premolars, being never interrupted as in A. perimense. In A. 
megalodus , as far as I can gather from Professor Cope’s description , 3 there is no 
* crochet ’ in the upper true molars, and the 6 cingulum 5 is wanting from the 4 poste- 
rior collis 5 of the premolars. 
The upper molars of A. meridianum 4 present a considerable resemblance to those 
of the Indian species. As far, however, as I can judge from the figure, they appear 
to differ by the greater development of the protuberance from the c anterior collis ’ 
into the 4 median valley’ in the premolars, and also by the simpler form of the 
‘ cingulum.’ 
A. mite 5 is readily distinguished from the present species by the fact of the 
4 colies 5 (‘ transverse crests ’ of Prof. Cope) of the premolars being united on the 
inner side, and by there being no 4 cingulum ’ on the inner surfaces of the true 
molars. 
In A. occididentale 6 the premolars present a very considerable resemblance to 
those of the present species ; the true molars are, however, readily distinguished by 
the absence of any distinct 4 crochet 5 and by differences in the form of the 6 cingu- 
lum.’ The upper molars of A. pacificism 1 are characterised by a small and con- 
tinuous 4 cingulum,’ and by the absence of a 6 crochet,’ and £ buttress ’ at the antero- 
external angle. Of A. truquianum I have been unable to discover a description of 
the upper molars. 
General characters of upper molars . — It has now been shown that, as far as 
the materials for comparison are available, the Perim Island acerothere seems to be a 
distinct species, and consequently, in treating of the other remains referred to 
that species, it will be unnecessary to institute comparisons between them and those of 
other species. In the upper molar dentition of A. perimense, the most noticeable 
general points are that the whole dentition is generally less specialised than that 
of Rhinoceros. This want of specialisation is shown in the general completeness and 
great development of the 4 cingulum,’ which is more marked in the premolars than 
in the true molars , 8 and is a character connecting the genus with the generalised 
i n Proceedings Acad. Nat. Sci. Philad.,” 1875, p. 260. 
3 “ ul. U. S. Geol. Geog. Surv.” vol. v., p. 237. 
3 “ U. S. Geol. Geog. Surv. of Colorado,” 1873, p. 52. 
4 “ U. S. Geog. Surv. W. of 100th Merid.,” vol. iv., pi. Ixxiii., fig. I. 
6 “ U. S. Geol. Geog. Surv. of Colorado,” 1873, p. 494. 
6 “ Jour. Acad. Nat. Sci. Phil.,” 2 Ser., Vol. VII., pi. xxii. {Rhinoceros occidentalis) . 
7 Leidy. “ Contri. to Ext. Vert. Fauna of West. Territories.” U. S. Geol. Surv.,” pi. II., fig. 6, 7 {Rhinoceros pad- 
ficus'). 
8 On page 15 of the first volume of this series it is stated by Mr. Foote that “in R . perimensis, Falconer, the 
guard (cingulum) is absent from the upper premolars.” It is difficult to see how this statement originated, since the 
only complete tooth figured by Falconer was a premolar with a most marked ‘ cingulum.’ The premolars of R. decca- 
nensis in respect of the presence of a large ‘cingulum,’ approach very closely to those of A. perimense ; the true molars 
of the latter have, however, a 1 buttress,’ which is wanting in the former. 
F 
