566 UNGULATES. 



feistent) and third premolars. The smaller extinct species {Hippopotamus 

 minor) has the same close resemblance in its dentition, and though 

 much reduced in size, yet in both the number (four) and the 

 cylindrical form of the procumbent lower incisors, it adheres to the 

 typical dentition of the Hippopotamus. 



205. Hexaprotodon. — The fossil Hippopotamus of the Sewalik 

 tertiary beds, had the same number of incisors as the Hog, viz : 

 six in both jaws, or ^ : those below are more equal in size than 

 they are in the Hippopotamus, the median being rather less than 

 the two outer incisors ; they are all more oblique in position and 

 the abraded surface is more confined to the extremity. The lower 

 tusks are relatively shorter (PI. 143, fig. 1, c). The first premolar 

 (p. 1) is retained longer than in the Hippopotamus : the second 

 {p 2) is removed from the third as in the European fossil Hippo- 

 potamus, but is relatively thicker ; the second and third deciduous 

 molars are retained in the specimen figured. The form of the true 

 molars, and the pattern of their grinding surface resemble those in 

 the true Hippopotamus. 



206. Merycopotamus{\). — In the true molars of the Merycopotamus 

 (PI. 140, fig. 8) the inner demi-cones, i i, are simply convex, and the 

 two grooves on the outer ones form a deep external depression, at the 

 bottom of which is the convex ridge, o o : the antero-posterior cleft 

 dividing the primary lobes, instead of being straight as in the Hippo- 

 potamus, forms two bends convex inwards, and thus the symmetrical 

 pattern of the Hippopotamic molar is converted into the double-cres- 

 centic one of the Ruminant molar. The cement at the bottom of the 

 valleys is thinner than in the Ruminants, the enamel is as rugose 

 as in the Giraffe or Sivathere ; but the strong rugged ridge along 

 the inner half of the base of the crown forms the chief distinction 

 between the molars of the Merycopotamus and those of the Ruminant. 

 The teeth in the lower jaw make a similar approximation to the 

 Ruminant type, but the anterior and posterior primary divisions 

 are separated by a wider cleft ; the last molar has a third hinder 

 lobe, the lower molars are implanted by two roots. The forms, 



(I) This genus, together with Hexaprotodon, was discovered in the sub-himalayan tertiary 

 deposits and determined by Capt. Cautley and Dr. Falconer. 



