222 mocEEDixGS or the geological society. [Apr. 3, 



tion. A last upper true molar, figured by Mr. Trimmer in the " Philo- 

 sophical Transactions' for 1833, pi. ix., agrees exactly with the homo- 

 logous leptorhine tooth from Lexden in the possession of the E-ev. 0. 

 Fisher, P.G.S., and proves the occurrence of that species in the brick- 

 fields of Brentford. It is quoted by Professor Morris*, on Professor 

 Owen's authorit}^, as tichorliine, from which, however, it differs in 

 all the points already enumerated. In the Museum at York I also 

 found evidence of the R. leptorliinus of Owen among the remains 

 found at Bielbecks Parm, near Market Weighton, described in the 

 * Philosophical Magazine ' for 1809. The suppression of the anterior 

 combing -plate, the large development of the guard, the pyramidal 

 shape of the collis, and the presence of the third cos^a present a combi- 

 nation of characters found in that species alone. Prom the same de- 

 posit were obtained the remains of the Cave-lion, "Wolf, Horse, Mam- 

 moth, Bison, Urns, and Bed Deer, 



5. Perynanent Lower Dentition. — The upper molar series in all 

 the species of Bhinoceros, both recent and fossil, presents character- 

 istics which enable us to detect the species from the examination of 

 a single isolated tooth. The lower molars, on the other hand, are 

 so remarkably alike in all the species that this is frequently impos- 

 sible. In this respect, however, the tichorhine can be differentiated 

 from the megarhine Bhinoceros, as I have already shown in my 

 essays on their dentition. The leptorhine lower molars differ from 

 the tichorhine in all those points by which the megarhine are charac- 

 terized. In both, the obliquity of the wear of the enamel on the 

 outer side of the crown- surface, caused by the overlapping of the 

 upper teeth, contrasts with the even wear of the corresponding part 

 of the tichorhine molars. In both, the first premolar (Pm. 2) is 

 trenchant, and the external lamina presents a smooth, horizontally 

 convex surface with a faint apical depression. The anterior valley 

 is faintly impressed, the posterior is extremely shallow. In pre- 

 molars 3 and 4 the median groove traverses the base of the external 

 lamina. The leptorhine lower molars can, however, be differentiated 

 from the megarhine by the coarser enamel-sculpture, and especially 

 by the flattening of the anterior area (m) of the external lamina. 

 These characteristics are found in all the lower teeth of H. lepto- 

 rhinus which have been derived from the bone-caverns of Kirkdale or 

 Durdham Down, and in all those which have been found in associa- 

 tion with upper teeth in river- deposits, as in those figured by Pro- 

 fessor Owen from Clacton and Walton, in Essex (Poss. Mam. figs. 

 12-136). Some non-tichorhine lower jaws, however, I am unable 

 to assign with certainty to the leptorhine, megarhine, or Etruscan 

 species. 



The differences which Professor Owen notes between the lower 

 teeth of the leptorhine and tichorhine species do not apply to their 

 permanent dentition, — the lower rami of the latter species from 

 Lawford and Thame, in the Oxford Museum, containing the milk- 

 series, while the lower rami of the former, with which they are 

 compared, present us with the permanent. "While fig. 136 (op), cit.) 

 * Quart. Journ. Greol. Soc. vol. yi. p. 204, 



