158 Transactions of Hue Society. 



dentition, and we were for a very long time unacquainted with any 

 older forms showing a more generalised type of structure. Until 

 about a year ago the only forms of Elephants with which we were 

 acquainted were (1) the African Elephant, (2) the Indian Elephant, 

 (3) the Mastodon, (4) the Tetrabelodon, and (5) the Dinothcrium. 

 The extinct forms of Elephant approach either the African or the 

 Indian type : for instance, the Mammoth agrees most nearly with 

 the modern Indian form ; the Mephas mcridionalis of the Norfolk 

 Forest Bed and other deposits suggests affinities with the African 

 species. Certain small pigmy forms, occurring fossil in Malta, 

 Sicily, and Cyprus, may also have had affinities with the African 

 species. But it is only in the molar teeth that these Elephants differ 

 in any material degree from one another. The Mastodon has the 

 character of the molars considerably changed from those of the 

 true Elephants. In the Indian Elephant and in the Mammoth, the 

 transverse ridges — which are placed closely together, forming the 

 massive molar teeth — have sometimes as many as tliirty ridges in 

 one tooth ; in some of the American Mastodons the molars had 

 only three ridges. Another peculiarity is the occasional presence of 

 milk-incisors in the lower jaw of the American Mastodon. Other- 

 wise, modern and extinct Elephants and Mastodons agree in having 

 only one pair of incisor teeth, and those always being in the upper 

 mandible. In Tetrabelodon, which was a Miocene form, two pairs 

 of incisors seem always to have been present, the upper pair being 

 bent downwards, and the lower pair being directed nearly straight 

 in front, or a little curved upwards. On account of the large size 

 of the molar teeth in modern Elephants, we usually find not more 

 than two molar teeth on each side in use in the jaws at the same 

 time ; these are renewed from behind — not from below, as in most- 

 other mammals, and in the earlier forms of Proboscidea — and are 

 pushed forward and worn away in front by the new molars 

 gradually taking their place from behind. In the earlier forms of 

 the Elephant and Mastodon, the teeth being smaller, a larger 

 number could be in use in the cheek-series at the same time than 

 in Eleplias ; in Tetrabelodon this is also the case. 



The gradual increase in the complexity of the proboscidean 

 molars is one of their most striking characteristics. We notice also 

 the loss of the incisors, only two upper ones remaining ; the canines 

 are also lost. In the earliest forms some at least of the cheek-teeth 

 are replaced by premolars in the usual manner ; these teeth remain 

 in wear simultaneously with the true molars, but in later forms no 

 vertical succession takes place, and as the milk-molars are worn 

 they are shed, being replaced from behind by the true molars. 



In Palcvomastodon (Upper Eoeene) the molars are trilophodont ; 

 in Moerithium the teeth are simple brachyodont bilophodont 

 (quadritubercular molars), and molars, premolars and incisors are 

 all present. In the earliest forms the skull had not attained the 



