246 



exact number of molar teeth in the lower jaw, which is twelve : of these 

 the three posterior teeth on each side are tuberculate or true molars ; 

 and the three anterior ones are compressed and conical, or false molars ; 

 the latter have each two roots and are relatively larger than in the Hog- 

 tribe. The tooth anterior to the grinders, and which from its shape 

 Cuvier regarded as a canine, is situated closer to the symphysis of the 

 jaw than in anv of the existing Suidce, : but the Peccari in this respect 

 also comes nearest to the Chaeropotamus. The grinders, as in the Peccari, 

 are narrower in the lower than in the upper jaw. On the outer surface 

 of the jaw, near its anterior extremity, the vascular foramina are as 

 numerous as in the jaws of the Hog-tribe. 



Genus Hyracotherium. 



1082. The skull, without the lower jaw, of the Hyracotherium leporinum, Owen. 



This unique specimen was discovered in the Eocene or London Clay 



at Heme Bay. Presented by William Richardson, £sq., F.G.S. 



The molars are seven in number on each side, and resemble more 

 nearly those of the Chaeropotamus than the molars of any other known 

 genus of existing or extinct Mammalia. They consist of four spurious 

 molars or premolars, and three true molars. The first and second 

 premolars, counting from before backwards, have simple subcompressed 

 crowns, surmounted by a single median conical cusp with a small 

 anterior and posterior tubercle at the outer side, and a ridge along the 

 inner side of its base : they are separated from each other by an inter- 

 space nearly equal to the antero-posterior diameter of the first molar, 

 which measures two lines and a half. The second and the remaining molars 

 are in close juxtaposition. The third and fourth false molars present a 

 sudden increase of size and of complexity of the grinding surface, with 

 a corresponding change of form. The plane or transverse section of the 

 crown is subtriangular with the base outwards and nearly straight, the 

 apex inwards and a little forwards, rounded off, to which the anterior 

 and posterior sides converge in curved lines ; the grinding surface sup- 



