MASTODON. 615 



in the British Museum, that only one of the lower tusks, usually 

 the right, was retained or succeeded by a permanent tusk in 

 the adult male (ib. fig. 14, i).(l) I first pointed out the inferior 

 tusks, whether transitory or persistent, as a well-marked generic 

 character of Mastodon, as contradistinguished from Elephas, in my 

 *' History of British Fossil Mammalia" (p. 275) ; and also defined 

 a second character, in the displacement of the first and second 

 molars, in the vertical direction, by a tooth of simpler form than 

 the second, a true * dent de remplacement', developed above the 

 deciduous teeth in the upper, and below them in the under jaw. 

 Both these dental characters, which are of greater importance 

 than many accepted by modern Zoologists as sufficient demarca- 

 tions of existing generic groups of Mammalia, have been recog- 

 nised in the Mastodon giganteus, of North America, and in the 

 Mastodon angustidens which is the prevailing species of Europe. 



The molar formula of the genus Mastodon, according to the 

 total number of grinders developed, is: — ^J = 28.(2) But in this 

 number are combined both the deciduous and permanent teeth, 

 contrary to the dental formulae of most other Mammalia. The 

 two series may, however, be distinguished in the Mastodon, not- 

 withstanding the successive fall of the true theoretically permanent 

 molar teeth. The first two molars in the upper jaw, for example, 

 are unequivocally proved to be the analogues of the deciduous teeth 

 in ordinary Pachyderms by their relation to a vertical successor, 

 premolar, or ' dent de remplacement.' There are good grounds 

 also, for regarding the third molar in the order of development, 

 as the last of the theoretically deciduous series, although it has no 

 vertical successor. According to these views of the teeth analogous 

 to the permanent series in ordinary Pachyderms, the formula of 

 Mastodon is : — 



1-1 1-1 N l-i //• X 0-0 1-1 3--3 



'^' ^0 °^ i^T (^«^)' ^ (Z-^^-') '■ 0-=;;' ^- 1=1' ^- i=i' = 20. 



(1) See ray Memoir on the so-called Missourium and Tetracaulodon, Proceedings of the 

 Geological Society, 1842, No. 87, p. 689- 



(2) The presence of the small premolar in the lower jaw has not yet been determined ; 

 neither has its absence. An excavation in the jaw of the young Mastodon described by 

 Dr. Godman, at the place where the germ of the premolar is hypothetically sketched in 

 PI. 144, fig. 7, p 1, would determine this point in regard to the M. giganteus. 



