MR. W. B. DAWKms ON RHINOCEROS MEGARHINTJS. 



411 



The posterior collis, F, is divided by a notch from the median in the 

 unworn tooth, and in place of bearing a cnsp is widely notched 

 apically. 



In the third molar (M 3) the second costa, K 2, of the external 

 lamina, L, is the higher, and the posterior area is slightly waved with- 

 out trace of ribs. The entrance to the anterior valley is very large 

 and wide, and is sometimes blocked up by a cusp, and the posterior 

 combing plate is very strongly developed. In the portion of the 

 anterior valley mapped off by it are accessory folds of enamel. The an- 

 terior coUis, D, is narrower than in the tichorhine species. The third 

 collis is represented by a small cusp as in the majority of the ticho- 

 rhine homologues. The guard on the anterior aspect is very 

 prominent. 



§ 4 B. Lower Molar Series. — The lower molar teeth (Eig. 14) 

 are so much like one another, with the exception of the first and last 

 of the series, that size alone is the clue to their exact position in the jaw 

 of the animal. In the premolar series the two valleys are V-shaped, 

 and at a higher level relatively than those of the true molars. 



The first premolar (Figs. 12, 13) is trenchant, and the external 

 lamina presents a smooth horizontally convex surface with a faint 

 depression apically. The anterior valley is faintly impressed, and the 

 posterior is extremely shallow, the inner surface of the tooth figured 

 presenting a flat square slightly undulating area. 



In premolars three and four the median groove traverses the base 

 of the external lamina, which it never does in the tichorhine homo- 

 logues. In premolars three, four, and true molar one, the inner 

 aspect of the tooth is much more hollowed than in the tichorhine or 

 leptorhine species. In the two latter a ridge passes down from the 



