336 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 8, 



position and value to Mr. Wigham's specimen, considering tlie latter 

 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 *." 



There is some intricacy in the terms expressive of the numerical 

 values which Prof. Owen assigns to the different molars of Mas- 

 todon in his descriptions, both 'in the ' British Fossil Mammalia,' 

 and in the * Odontography.' This, I believe, has arisen from the 

 peculiar viev/s 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 be- 

 tween Mastodon and Dinofherium, I think it desirable to make a few 

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

 that Mastodon is distinguished from Elephant, in a well-marked and 

 unequivocal manner, by two dental characters : the first is the pre- 

 sence 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 angus- 

 tidens, which are much worn, and are true deciduous teetli, the only 

 ones, in fact, which strictly correspond with the deciduous teeth of 

 ordinary Pachyderms |:." In this view, when the ante-penultimate 

 and penultimate milk-molars are shed, and the penultimate premolar 

 has made its appearance, he designates the latter as the *' third 

 molar tooth ; " and the last milk-molar, which is behind it in posi- 

 tion, 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 ver- 

 tical 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' §. M. Lartet has found the same two premolars re- 

 peatedly in the upper and lower jaws of M. {Trilophodon) angus- 

 tidens || . In a manuscript note appended to the work here quoted, 

 with which 1 have been favoured by M. Lartet, he adds, *' J'ai 

 pu depuis lors verifier plusieurs fois le remplacement eifectif de la 

 2™^ et de la 3™*^ molaire de lait, tant a la machoire superieure qu'a 



* hoc. cit. 



t Brit. Foss. Maniin. p. 274, and Odontography, p. 615. 



X Brit. Foss. Mamm. p. 284. 



§ Op. cit. p. 31, pi. 6. f. 4-6 ; pi. 12. f. 8^11. 



II Lartet, Notice sur la Colline de Sansan, 1851, p. 25. 



