420 HYRACOTHEKIUM. 



from any living Mammalia, and to have had the nearest 

 affinity to the Chceropotamus. 



The fossil in question consists of a mutilated cranium 

 (fig. 1 65) rather larger than that of a hare, containing the 

 molar teeth of the upper jaw nearly perfect and the sockets 

 of the canines. It was discovered in the London clay 

 forming the cliffs at Studd Hill, about a mile to the west 

 of Herne Bay, by William Richardson, Esq., F.G.S., who 

 kindly gave me the opportunity of describing it in the 

 Geological Transactions for 1839.* 



The molars are fourteen in number in the upper jaw, and 

 resemble more nearly those of the Choeropotamus than the 

 molars of any other known genus of existing or extinct 

 Mammalia. They consist of four premolars and three true 

 molars on each side. The first and second premolars, count- 

 ing from before backwards, have simple sub-compressed 

 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 se- 

 parated from each other by an interspace nearly equal to 

 the antero-posterior diameter of the first premolar, which 

 measures two lines and a half. The second and the rest 

 of the series are in close juxtaposition (fig. 166). The 

 third and fourth premolars present a sudden increase of 

 size and of complexity of the grinding surface, with a cor- 

 responding change of form : their grinding surface supports 

 three principal tubercles or cusps, two on the outer and 

 one on the inner side : there are two smaller elevations, 

 with a depression on the summit of each, situated in the 

 middle of the crown, and the whole is surrounded by a 

 ridge, which is developed into a small cusp at the anterior 

 and external angle of the tooth. These teeth form the 



* Geol. Trans., Second Series, vol. vi. p. 203. 



