MASTODON ARVERNENSIS. 



37 



to be the ' second true molar.' In our view they are both 

 last milk molars, which would be the equivalent of what 

 Prof. Owen designates as ' the fourth in the order of size, 

 and the third in the order of position, counting backwards in 

 the upper jaw, before any of the teeth are shed.' 1 



There is some intricacy in the terms expressive of the 

 numerical values which Prof. Owen assigns to the different 

 molars of Mastodon in his descriptions, both in the ' British 

 Fossil Mammalia' and in the 'Odontography.' This, I 

 believe, has arisen from the peculiar views there advanced 

 as to the order of succession of the premolar teeth in this 

 genus ; and as it is a point of systematic and palseontological 

 importance in reference to the disputed affinities between 

 Mastodon and Dinotherium, I think it desirable to make a few 

 remarks on the subject. In both the works here cited, 2 it is 

 affirmed that Mastodon is distinguished from Elephant, in a 

 well-marked and unequivocal manner, by two dental charac- 

 ters : the first is the presence of tusks in the lower jaw ; the 

 second ' is the displacement of the first and second molars ' 

 (meaning milk molars) ' in the vertical direction by a tooth 

 of simpler form than the second, a true dent de r -emplacement, 

 developed above the deciduous teeth in the upper, and below 

 them in the under jaw.' Prof. Owen, in his remarks upon 

 Mr. Fitch's specimen of the last milk molar (fig. 100), goes 

 on to say, ' In Dr. Kaup's figure the tooth in question ' (i.e. 

 the third) ' is associated with the first and second molars of 

 the Mastodon angustidens, which are much worn, and are 

 true deciduous teeth— the only ones, in fact, which strictly 

 correspond with the deciduous teeth of ordinary Pachy- 

 derms.' 3 In this view, when the antepenultimate and 

 penultimate milk molars are shed, and the penultimate pre- 

 molar has made its appearance, he designates the latter as 

 the ' third molar tooth ;' and the last milk molar, which is 

 behind it in position, but anterior in appearance, he calls the 

 ' fourth molar tooth,' although fully aware that there were 

 good grounds for regarding it ' as the last of the theoretically 

 deciduous series, although it has no vertical successor.' 

 But this conclusion as to the absence of a vertical successor 

 to the tooth in question was premature. I detected both the 

 penultimate and last premolars in situ in the jaws of E. 

 (Loxodon) planifrons, a Sewalik fossil Elephant, upwards of 

 twelve years ago. The evidence is published in the ' Fauna 

 Antiqua Sivalensis.' 4 M. Lartet has found the same two 

 premolars repeatedly in the upper and lower jaws of M. 



1 Op. cit. p. 284. 4 Op. cit. p. 31, PL vi. figs. 4-6 ; PI. xii. 



2 Brit.Foss.Mamm.p. 274; and Odon- figs. 8-11. (See vol. i. pp. 68, 427, 

 tography, p. 615. and 433.— Ed.) 



3 Brit. Foss. Mamm. p. 284. 



