ME. W. B. DIWKTNS OTf RHINOCEROS MEaARHINTTS, 



405 



A comparison of figures 1 and 2 with Eig. 1 of PI. iii. of the 

 Nat. Hist. Eev. for 1863, will show at a glance the difierence between 

 the megarhine and the tichorhine first milk molars. 



The second upper milk molar (Dm 2, Fig. 3 and 5) is difi'eren- 

 tiated from its homologue in the tichorhine species by its size, and by 

 the smoothness of its posterior area, N. The external lamina, 

 L, bears two costse, K 1 and K 2, of which the second is the higher, 

 and is divided from the broad first by a depression that passes 

 obliquely hackwai^ds from the base to the summit of the crown. 



The anterior collis, D, equals the posterior in size, and is not 

 divided by a cleft from the external lamina as in R. tichorhinus. 

 (Conf. Nat. Hist. Eev. 1863, PI. iii. Fig. 2). The anterior valley has 

 a wide entrance. In one specimen the accessory valley C is mapped 

 off by two combing plates that meet and become fused. In a second 

 the head of the anterior valley is traversed by two involutions of 

 enamel. The posterior wall of the tooth, F, or the third collis (Collis 



^/ 



M^ 



^4 



M^.^. 



tertius of Brandt,) is depressed in its middle part, and without a 

 cusp in the 2nd, 3rd and 4th milk molars. 



