388 



PALEONTOLOGY. 



d 



Fig. 141. 



Upper molar of Mastodon avernensis. 

 marine crag, Norfolk. 



Fluro- 



tiiiguisli the extinct genus, in respect of the structure of the 

 molar teeth ; the dentine, or principal substance of the 

 crown of the tooth (fig. 141, d) is covered by a thick coat ol 



dense and brittle en- 

 amel (e) ; a thin coat 

 of cement is con- 

 tinued from the 

 fangs upon the crown 

 of the tooth, but this 

 substance does not 

 fill up the inter- 

 spaces of the divi- 

 sions of the crown, 

 as in the elephant's 

 grinder (fig. 146, c). Such at least is the character of the 

 molar teeth of the two species of Mastodon, which Cuvier 

 has termed Mastodon giganteus and Mastodon angustidens 

 (fig. 141). Fossil remains of proboscidians have subse- 

 quently been found, principally in the tertiary deposits of 

 tropical Asia, in which the number and depth of the clefts of 

 the crown of the molar teeth, and the thickness of the inter- 

 vening cement, are so much increased as to establish transi- 

 tional characters between the lamello-tuberculate teeth of the 

 elephants and the mammilated molars of the typical Masto- 

 dons, shewing that the characters deducible from the molar 

 teeth are rather the distinguishing marks of species than of 

 genera in the present family of mammalian quadrupeds. 



The dentition of this family may be expressed by the 

 formula — 



at , t L1 , c , a m 3 3 , p 1A , m 3 - 3 _ .j-± , 



that is to say, in the Proboscidians in which the dentition 

 most nearly approached to the typical one, thirty-four teeth 

 were developed, as follows : — in the upper jaw, two deciduous 



