PREPACE. 
Xlll 
If the lower jaw assigned to R. simlensis in the “ Eauna Antiqua Sivalensis ” 
he rightly assigned, and if we admit the sub- divisions into which the old genus 
Rhinoceros is split up by many modern naturalists, R. simlensis would seem from 
this point of view to belong to the genus Atelodus characterized by the symphysis 
of the mandible of the adult being edentulous, as in Rhinoceros simus. The skull 
of R. sivalensis is, however, unicorn, and, therefore, differs from that of R. simus. 
The species in fact, if the remains are rightly correlated, will not fit into any of 
the modern sub-divisions of the genus. 
Rhinoceuos ieavadictjs. — The fragment of a right maxilla of a species of 
Rhinoceros with two teeth described on page 45, and figured in Plate V, fig. 4, 
of this volume, which was not specifically determined, and the teeth in which were 
considered to be premolars, I now find to belong to a young individual with the milk- 
molar dentition. It appears probable that these milk-molars may have belonged to 
a young individual of Rhinoceros iravadicus, the permanent molars of which species 
are figured on the same plate ; in having a combing plate they are more complex 
than the true molars. 
Aceeotherium perimense {Rhinoceros planidens). — As I have already men- 
tioned in the “ Records,”^ the two imperfect upper molars of a rliinoceros figured 
on Plate IV, figs. 7 and 9, and described on page 41 of this volume, as belonging 
to a new species of Rhinoceros, under the name of R. planidens, really belong to 
Acer other ium perimense of Ealconer and Cautley. The upper teeth of that species 
figured on Plate VI, figs. 2 and 5, as upper true molars, really are premolars, and 
the unnamed specimen represented in fig. 6 of the same plate is likewise an upper 
premolar of the same species.^ The name of R. planidens must accordingly be 
erased from the list of Asiatic species of Rhmoceros given on page 52, and the 
description of its upper molars be read as those of A. perimense. In a subsequent 
volume I shall hope to illustrate more fully the dentition and craniology of the 
last named species : a cranium is now in the collection of the Indian Museum. As 
the teeth of this species, described on page 51 as molars, are really premolars, the 
statement as to the difference in shape of the molars of this species from the molars 
of Rhinoceros will consequently not stand. 
It is at present unknown whether Acerotherium perimense was furnished witli 
three or four digits to the forelimb, and from the condition in which Siwalik fossils 
usually occur, it is very improbable that this point will ever be determined. It is, 
therefore, impossible to say whether the species really belongs to Acerotherium or to 
the new genus Aphelops of Professor Cope,® differing from Acerotherium in having 
only three anterior digits. I prefer provisionally to retain the species in the older 
genus. • 
* Vol. XII, p. 47. 
^ On page 44 I mentioned that I thought it possible this tooth should he referred to R. 'planidens (A. perimense). 
The cingulum is remarkably developed in this tooth, and causes it to resemble the premolars of R. deccanensis, as 
noticed in the description. 
® Bull. U. S. Geol. Geog. Surv., Vol. V, p. 236. 
