siwalik bhinocebotida:. 
9 
sented on plate VIII. Very generally, in this type an ‘accessory fossette,’ formed 
in the manner noted above, is present ; while a ‘ crochet ’ and ‘ combing-plate ’ seem 
to be always present, whether they unite or not. In certain species, as in the Siwa- 
lik R. palceindicus , the upper molars seem to be intermediate in character between 
those of the two types mentioned above ; these will be occasionally referred to below 
as the * intermediate type.’ 
Genus I. ACEBOTHEBIUM, Kaup. 
(Including Aphelops, Cope.) 
The genus Acerotherium (with which Professor Cope’s genus Aplielops is in- 
cluded), established in 1832 by the late Professor Kaup 1 for the reception of a 
hornless and anteriorly four-toed species of rhinoceros, may be shortly defined as 
follows : — No horns in either sex ; nasals thin and pointed* and their upper surface not 
differentiated from that of the frontals. Anterior limbs either tri — or tetradactyle ; 
incisors present in both jaws. 2 
Species : Acerotherium pebimense, Ealconer & Cautley sp. 
Synonyms : Rhinoceros (Acerotherium ?) perimensis, Falc. & Caut. 
Rhinoceros planidens, Nobis. 
Rhinoceros iravadicus, Nobis. 
Earlier notices. — The present species of hornless rhinoceros was first named by 
Ealconer and Cautley on the evidence of some mostly imperfect molars, and a part 
of a lower jaw obtained from the ossiferous beds of Perim Island, in the gulf of 
Cambay. These specimens are figured in plate LXXV of the “Eauna Antiqua 
Sivalensis,” and their provisional or hypothetical reference to the genus Acero- 
1 “ Isis.” Dresden, 1832. — The definition of the genus here given is adapted from the one given by the late Professor 
Brandt (Mem. d. 1. Acad. Imp. d. S. Pet., Ser. VII., Vol. XXVI, p. 27). Following Professor Brandt, the genus 
Aphelops of Professor Cope, distinguished from Acerotherium by having three in place of four digits on the fore-limb, 
is here included in Acerotherium, as in the majority of cases the number of digits cannot be determined. 
* According to Professor Cope (“ Bui. U. S. Geol. Geog. Survey,” Vol. V, p. 235), the genus Acerotherium is 
characterised by the presence of two pairs of both upper and lower incisors (the outer pair of the latter termed canines) 
and by the non-union of the post-tympanic and post-glenoidal processes of the squamosal below the external auditory 
meatus. With regard to the presence of two pairs of upper incisors being characteristic of the genus, it may first of 
all be observed that two pairs of these teeth are developed in Rhinoceros sclileiermacheri (Kaup. “Oss. Foss. d. 
Darmstadt,” pi. X, fig. 1), and occasionally in It. indicus (Lydekker, J. A. S. B., Vol. XLIX, pt. II, pi. VII, fig. 1) ; 
and secondly, that in Acerotherium incisivum there appears to be only one pair of upper incisors, as I judge from a 
cast of a skull in the Indian Museum, and from the figure given by Professor Gaudry- (“ Les Enchainements du Monde 
Animal, etc.” p. 47, fig. 38) ! Again, in the lower jaw of the same species, only the outer pair of incisors (canines) seem 
to be developed ( see Gaudry, loc. cit., p. 51, fig. 46) ; and only this pair are present in the Indian A. perimense. As 
far as I am able to judge from the cast of the skull of A. incisivum , the post-tympanic and post-glenoidal processes 
appear to be united interiorly. Professor Cope is therefore, to say the least, unfortunate in the characters he has 
selected for generic distinction. 
c 
