328 



RHINOCEROS. 



1. 



o 



Another character of much importance, as a specific dis- 

 tinction, is that the premolars of the Rhinoceros of the Gower 

 Caves are constantly devoid of an internal basal bourrelet. 



Having regard to the various points above indicated, the 

 premolars of R. hemitoecJms may be characterized : — 



By the absence of an internal basal bourrelet. 



By there being two fossettes only to the worn crowns. 



3. By the middle valley being traversed by the processes 



of a bifid crochet emitted from the posterior barrel, 

 and by a parallel combing plate given off by the 

 outer or longitudinal ridge. 



4. By being invested, like the true molars, with a very 



thick coat of cement. 



The presence of only two fossettes instead of three at 

 once distinguishes these premolars from those of Rhin. 

 tichorhinus, while the absence of a basal bourrelet, besides 

 other characters, distinguishes them from Rhin. megarhinus 

 and Rhin. leptorhimis. Among existing species, Rhin. bicornis 

 resembles the Gower fossil, form in the bifid crochet and 

 combing plate which project into the ' cul de sac ' of the 

 middle valley ; but it differs materially in the strongly 

 developed crenated bourrelet, which encircles the inner side 

 of the premolars. 



De Christol has figured two varieties of the last upper 

 premolar in Rhin. megarhinus, in one of which (fig. 10 of 

 PI. III.) there is a very pronounced basal bourrelet, while 

 the other (fig. 4 of PL III.) is entirely free from it (PL XVIII. 

 figs. 1 and 2 of this work). 1 The teeth correspond so exactly 

 in every minute detail of pattern in other respects, that it is 

 impossible to doubt that they are of the same species. The 

 tooth, fig. 4, agrees also with the last premolar of Rhin. 

 hemitoechus (p.m. 4 of fig. 1, PL XVI.), in the absence of a 

 bourrelet, in the 'crochet' being bifid, and in emitting a 

 single combing plate from the outer ridge. But' on insti- 

 tuting a minute comparison, the following points of dif- 

 ference are discernible. In the premolars of Rhin. megar- 

 hinus and also of Rhin. bicornis the ' combing plate ' (R. of 

 figs. 10 and 4 of De Christol) is emitted in a line with the 

 anterior outer angle, and converges diagonally to meet the 

 plane of the crochet (T.) nearly at a right angle ; and the 



1 Annales des Sciences Nat. 2me Ser. 

 torn. iv. Zool. In Dr. F.'s MSS. the 

 figures cited from De Christol are ' figs. 

 25 and 19,' which correspond to figs. 10 

 and 4 in PL III. of the memoir in the 

 ' Annales des Sciences,' there being 

 seven figures in PI. I., eight in PI. II., 



and fifteen in PI. III. The latter 

 figures, moreover, correspond with copies 

 which Dr. F. had made from those 

 numbered 25 and 19. These figures 

 have been reproduced in figures 1 and 2 

 of PI. XVIII. of this work.— [Ed.] 



