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,+ 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. iy. (1833.) + Loc. cit. 
+ 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. 
