326 RHINOCEROS. 



the exception of the small and deciduous first premolar, 

 which is rarely seen in situ. 



Premolars. — The premolars (PL XVI. fig. 1, p.m. 2, 3, 

 and 4) in R. hemitoechus belong to the series indicated by 

 Cuvier, in which there are only two fossettes produced by 

 wear on the grinding surface. The antepenultimate (p.m. 2) 

 presents a nearly square crown ; and the median termination 

 of the transverse valley is reduced to a triangular fissure, 

 which on the inner side is not quite isolated, the anterior 

 and posterior divisions not been ground down sufficiently to 

 efface the intervening cleft. The posterior valley is isolated 

 and reduced to an elliptical fossette. 



The penultimate premolar (p.m. 3), as is usual in the 

 genus, presents a sudden and very considerable increase of 

 size beyond the antepenultimate. Tbe inequalities of the 

 crown are worn down to a common plane, the middle of 

 which is occupied by a large and irregular fissure, being the 

 isolated termination of the middle valley ; and a round 

 fossette indicates the remains of the posterior valley. The 

 hinder boundary of the middle fissure forms a flexuous edge 

 composed of two projecting rounded lobes, being the remains 

 of a bifid ' crochet.' Several small tubercles are seen rising 

 up from the bottom of the fissure. 



The last premolar (p.m. 4) is presented in three different 

 stages of wear by the different specimens. In the ' Bacon 

 Hole ' fragment (PI. XVII. figs. 1 and 2), the abrasion of the 

 crown (p.m. 4) is so little advanced that the posterior 

 valley is not yet isolated ; the anterior and posterior barrels 

 are separated by a wide and deep valley, which is nearly 

 straight and of uniform width. Its posterior boundary is 

 undulated, but free from any considerable projection directed 

 from the posterior towards the anterior barrel. A portion of 

 the termination of the middle valley is already detached, 

 forming a third fossette. This, however, is an individual 

 variety, that is not uncommon in either the penultimate or 

 last premolars of species which have ordinarily but two 

 fossettes. It occurs occasionally in the premolars of R. 

 bicornis, and Gervais has figured an instance of the same 

 kind occurring in a premolar of R. megarhinus. The portion 

 of the crown corresponding with the outer or longitudinal 

 ridge is broken off, in this specimen ; but the loss does not 

 interfere with the principal character. 



A more advanced stage of wear and a different pattern 

 are seen in the same tooth (p.m. 4) as presented by fig. 1 

 of PI. XVI. The posterior valley forms a large detached 

 oval fossette. The inner side of the crown is worn so low 

 that the barrels are almost confluent, and the commencement 



