40 BRITISH AND EUROPEAN FOSSIL MASTODONS. 



Lower jaw. — The characters furnished by the lower jaw are of 

 great significance in distinguishing the nearly allied species of 

 Mastodon, more especially in what relates to the form of the 

 symphysis, and the presence or absence of mandibular incisors. 

 The differences between the lower jaws of M. (Trilophodon) 

 angustidens, M. (Tetraloph.) longirostris, and M. (Tetraloph.) 

 Arvernensis are so pronounced that they would have been 

 sufficient to discriminate the species, supposing the moiar teeth 

 were unknown to us. As above stated, no good specimen, so 

 far as I am aware, has hitherto been discovered of the lower 

 jaw of the Crag species, M. (Tetr.) Arvernensis, in England ; 

 but several have been met with in the Pliocene strata of 

 Italy and France ; while abundant remains of the lower jaw 

 of M. (Tetraloph.) longirostris have been disinterred from the 

 Epj>elsheini sands by Dr. Kaup, and of M. (Trilophodon) 

 angustidens by MM. Lartet and Laurillard from the Falunian 

 deposits of the Sub-Pyrenees. 



First in regard to If. (Triloph.) angustidens. The lower 

 jaw of this species is at once distinguished by the great elon- 

 gation, downward direction, and slender form of the symphy- 

 sial portion, which contains the sockets of the two inferior in- 

 cisors (Plate II. fig. 3). 1 The ascending ramus is of moderate 

 height, corresponding in that respect with M. (Trilophodon) 

 Ohioticus (fig. 2), and approaching that of Dinotherium gigan- 

 teum (fig. 1). The horizontal ramus is very high in front, in a 

 line with the mentary foramen, and low behind ; the anterior 

 portion is compressed ; and the lower margin stretches some 

 way in front of the mentary foramen, in a straight line ; it is 

 then bent a little downwards, and continued forwards in nearly 

 the same straight line ; the under surface of the elongated 

 portion forming an obtuse angle with the corresponding 

 surface of the horizontal ramus. The elongation of the 

 symphysial beak is enormous, far exceeding that of M. (Tetr a - 



an illustration of its presence in the 

 latter species, on one side of the lower 

 jaw, regarding it as a ' supernumerary 



numerical category, is exhibited in the 

 descriptions of the Elephants given 

 throughout by De Blainville in his 



tooth; and a corresponding occurrence | 'Osteographie;' and more recently in the 

 in the lower jaw of the same species is j otherwise excellent descriptions by Ger- 

 represented in the 'Fauna Antiqiia ' vais of the dentition of Mastodon Andium 



Sivalensis' (PI. xiv. fig. 4 a). It is usually- 

 restricted to one side, and I regard it 

 as not very uncommon. As the true 

 molars never exceed, nor are below, 

 three in number in the Pachydermia 

 and Ruminantia, the same terms may be 

 conveniently used in describing them. 

 The inconvenience of designating the 

 molars in Mastodon and Elephas by 

 successive numbers ranging from 1 to 

 6 or 7, which include both milk and true 

 molars without distinction in the same 



in the ' Expedition de Castelnau.' The 

 penultimate and last milk molars are 

 there figured and described as the 'third' 

 and 'fourth' molars, involving a confusion 

 of the ridge-formula, which is seen to be 

 of so much importance in the subgeneric 

 distinctions. (Recherches sur les Mam- 

 miferes Fossiles de l'Amerique Meridio- 

 nale, 1855, pp. 20-22, PL v. figs. 1-5.) 

 „ ' De Blainville, ' Osteographie : Des 

 Elephants,' PI. xiv. 



