334 RHINOCEROS. 



triangular in form, separating the inner hind barrel from the 

 posterior termination of the outer ridge. This fissure forms 

 the posterior valley. All the species of Rhinoceros hitherto 

 described may be ranged under two heads : 1. Those in which 

 the last true molar has a posterior valley ; 2. Those in 

 which it is wanting. To the former series belong Bhin. 

 tichorhinus and Bhin. simus, which further agree in the 

 common character of presenting three fossettes to the worn 

 crown of the last true molar, namely : one fossette, formed by 

 the posterior fissure ; the second, caused by the confluence of 

 the crochet with the combing plate intercepting a portion of 

 the transverse valley ; and a third fossette, formed by the 

 remaining or open portion of the latter valley. To the second 

 series belong the unicorned and bicorned species of Asia, and 

 the African Bhin. bicornis, together with the European fossil 

 species, such as Bhin. megarhinus, Bhin. leptorhinus, Cuvier, 

 Bhin. Schleiermacheri, &c. They all agree in the common 

 character of the posterior valley or fossette being wanting, 

 but are susceptible of being divided into two subordinate 

 series, namely, those in which the last molar presents two 

 fossettes ; one formed by the confluence of the crochet with 

 the ' combing plate ' intercepting the outer portion of the 

 transverse valley, the other, composed of its open or inner 

 portion. This series is exemplified by Bhin unicornis among 

 living forms. The second subdivision includes the forms in 

 which the crochet is free from adhesion to the 'combing 

 plate,' and the crown, during wear, only exhibits a single 

 fossette, namely, the sinuous fissure of the transverse valley. 

 To this series belong the unicorned Rhinoceros of Java, Bhin. 

 bicornis, and the majority of the European fossd forms. The 

 last true molar may therefore be presented with one fossette, 

 as in Bhin. megarhinus (vide Gervais, Paleontol. Franchise, PI. 

 II. figs. 6 and 7) ; with two fossettes, as in Bhin. unicornis 

 (vide Cuvier, Oss. Eossiles, Bhin., PI. II. fig. 3) ; or with three 

 fossettes, as in Bhin. tichorhinus (op. cit. PI. VI. fig. 4). 



The presence or absence of the posterior or third fossette 

 entails an important difference in the form of the crown of 

 the last molar. When present (vide the fig. last cited), the 

 outline of the tooth is still four-sided, although the posterior 

 side is considerably reduced in width, and the separation of 

 the hind barrel from the end of the outer colline is distinctly 

 marked by an intervening fissure. But when the posterior 

 valley is wanting, the outline of the crown becomes triangular; 

 the summit of the anterior transverse colline remains as 

 usual, while the outer colline is directed diagonally inwards 

 and backwards, so as to make an acute angle with the former. 

 The result is that the summit of the crown, instead of being 

 rectangular, is Y-shaped, and the posterior transverse colline 



