HIPPOPOTAMUS. 399 



Europe and North America. It is remarkable that no equine 



Fig. 152. 

 Dentition of lower jaw, horse. 



animal existed in the New World at the time of its dis- 

 covery by Columbus and his followers. 



Genus Hippopotamus, L. — The discovery, in lacustrine and 

 fluviatile deposits of Europe, of the remains of an amphibious 

 genus of Mammal, now restricted to African rivers, gives scope 

 for speculating on the nature of the land which, uniting Eng- 

 land with the Continent, was excavated by lakes and inter- 

 sected by rivers, with a somewhat warmer temperature than 

 at present, to judge by a few S. European shells which occur 

 in the fresh-water formations — -e.g., at Grays, Essex, where 

 remains of the large extinct Hippopotamus major have been 

 found. The specimen of the lower jaw (fig. 154) was dis- 

 covered in the ' Forest bed," below glacial clay, on the Norfolk 

 coast. Other localities are specified in the writer's " History 

 of British Fossil Mammals," 8vo, 1846. 



The first premolar has a simple subcompressed conical 

 crown, and a single root ; it rises early, and at some distance 

 in advance of the second premolar, and is soon shed ; the 

 second (ib., p, 2) stands a little apart from the third ( 3 ). This 

 and the fourth premolar retain the simple conical form, but with 

 increased size, and are impressed by one or two longitudinal 

 grooves on the outer surface, which, when the crown is much 

 worn, give a lobate character to the grinding surface. The 

 true molars (m, 1, 2, 3) are primarily divided into two lobes 

 (fig. 153) by a wide transverse valley, and each lobe is -lib- 

 divided by a narrow antero-posterior cleft into two half cones. 



