MASTODON ARVERNEXSIS. 41 



lophodon) longirostris, or even of Dinotherium ; the length 

 from the mentary foramen forwards being more than double 

 that of the horizontal ramus, measured from the same point 

 backwards to the base of the anterior margin of the coronoid 

 process. A constant character of the species is the presence 

 in both sexes of two long, closely adpressed, and straight, or 

 but slightly curved, incisors. This fact has been established 

 by M. Lartet upon a very large number of specimens. 1 



These lower incisors differ notably in form from the upper. 

 In the adult specimens they are nearly of uniform diameter 

 from the base to the point, which is bevelled on the upper 

 side by wear, so as to yield a flat or spathulate surface. In 

 section they are pyriform, with frequently a longitudinal 

 channel on the upper and inner side. The section closely 

 approaches that of the inferior canines of the fossil Hippopo- 

 tamus named Hexaprotodon Sivalensis. The tusks or upper 

 incisors of this species are nearly circular in section, and 

 taper gradually to a conical point. They are invested along 

 their length on the inner side by a broad band of enamel, 

 which runs in an obsolete spire, so as to be presented on the 

 upper surface near the tip. M. Lartet has never observed 

 any indication of a belt of enamel on the lower incisors. In 

 the superb complete skeleton which was disinterred by Lauril- 

 lard at Seissan, the extruded portion of these lower incisors 

 measures 204 inches, that of the upper tusks being 41 inches. 

 The characters above indicated are constant, wherever the 

 lower jaw of this species has been discovered — whether in the 

 Faluns of the Orleannais and Touraine, in the lacustrine 

 deposits of G-ascony and Languedoc, or in the Miocene Molasse 

 of Switzerland, where I found them confirmed by the 

 examination of two very fine specimens, young and old, found 

 in the neighbourhood of Winterthur. They are well shown by 

 the representations given in De Blainville's 'Osteographie: des 

 Elephants,' PI. XIV. The molar teeth in all these specimens 

 have constantly presented the normal marks of the Trilopho- 

 don division — namely, three ridges to the last milk molar, and 

 to the antepenultimate and penultimate true molars. 



In M. (Tetrcdophodon) longirostris the ascending ramus is 

 considerably more elevated than in M. (Triloph.) angustidens, 

 approaching more the character which is seen in the 

 Elephants proper ; the horizontal ramus is less compressed 

 and more circular in section ; instead of presenting the 

 greatest height in a line with the commencement of the 

 alveolar border, or mentary foramen, it is contracted there 

 in consequence of the lower margin rising upwards to slope 



1 Lartet, ' Notice sur la Colline de Sunsan,' p. 2-i. 



