MASTODON ANGUSTIDENS. 293 



gigantic Mastodon, and that the tusks were merely milk- 

 teeth, which were lost as the animal became adult."* 

 This opinion was opposed by Dr. Hays in an elaborate 

 memoir, *f ad hoc ; and, with regard to a suggestion 

 offered by Mr. Peale, that the tusks on the lower jaw 

 might be only a sexual distinction, Dr. Hays expresses his 

 opinion, " that it is impossible in the existing state of our 

 knowledge, and with our present materials, to confirm or 

 positively refute this suggestion." 



Availing myself of the rich accession of evidences of the 

 osseous and dental organization of the Mastodon giganteus, 

 collected in the Missouri territory in 1840, and brought to 

 this country in the following year by Mr. Albert Koch, 

 I arrived at the conclusion that the Tetracaulodon of Dr. 

 Godman was the immature state of both sexes of the 

 Mastodon giganteus of Cuvier, and that in the male, one 

 at least, and usually the right, of the two lower tusks was 

 retained, but that in the female both were lost as she 

 approached maturity.^ The inferior tusks, with some 

 modifications of the grinding teeth, which I regard as in- 

 dividual varieties, have, nevertheless, been since interpreted 

 as establishing not only the Tetracaulodon, but as character- 

 izing six distinct species of that genus. 



Apart from the considerations of the dental charac- 

 ters leading to such opposite conclusions respecting the 

 mastodontal fossils from North America, the theory of the 

 unity of the species, of which the inferior tusks were regard- 

 ed by me as immature and sexual characters, might have 

 met with a less general reception than has been accorded 



* Silliman's Journal, vol. xix. (1830), p. 159, quoted by Dr. Hays in Trans, 

 of Amer. Phil. Soc. vol. iv. (1833.) f Loc. cit. 



t Proceedings of the Geological Society, Feb. 1842. The specimens de- 

 scribed, and from which the above conclusions were drawn, are now in the British 

 Museum. Proceedings of the Geological Society, June 15,1842. 



