ELEPHANT AND MASTODON. 23 



to belong to the 'milk,' and the rest to the permanent series. 

 These teeth resembled, in every respect, molars of the same size, 

 in other specimens of the lower jaw, which exhibited no vestige of 

 a tusk, and which were usually considered to belong to M. Ohio- 

 ticus. Mr. W. Cooper, in consequence, immediately questioned 

 the accuracy of Godman's inference, and insisted that the inferior 

 tusks indicated merely differences dependent on age and pro- 

 bably sex ; that they were possessed by the young animals, but 

 were shed during the increase of age, the period of their fall vary- 

 ing with the individual. 1 Mr. Titian Peale suggested that these 

 inferior tusks might be a distinctive mark of young males. 3 Dr. 

 Harlan adopted the same view, 3 and referred to the corneous 

 appendages in several genera of the Ruminantia as analogous 

 distinctive characters between males and females. Notwithstanding 

 the force of these objections, Dr. Isaac Hays, in 1831, not merely 

 maintained the correctness of Dr. Godman's opinion regarding the 

 distinctness of Tetracaulodon, but attempted to distinguish two 

 additional species of this nominal genus under the titles of T. Col- 

 linsii and T. Godmani, besides two new North American species 

 of Mastodon} The memoir in which these opinions were ad- 

 vanced, is illustrated by an excellent and copious series of figures, 

 exhibiting the dentition of M. Ohioticus, from a very early to the 

 adult stage ; and although Dr. Hays has entirely failed in sustain- 

 ing the genus Tetracaulodon, or the species which he proposed, 

 his memoir has served as an important contribution to palaeon- 

 tology, by showing that the number of molars developed during 

 life, in M. Ohioticus, successively from behind, amounts to six. 

 These he has traced, from the first to the last with great care, in 

 the lower jaw, and established the position and characters of each 

 by the comparison of a large number of specimens. 



1 W. Cooper, 'Lyceum of Nat. History of New York,' April 1830; 'Silliman's 

 Journ.' vol. xix. p. 159 ; and Featherstonhaugh's ' Monthly Americ. Journ. of Geol.' 

 vol. i. p. 158. 



2 Titian R. Peale, quoted in Dr. Hay's Memoir Amer. Phil. Trans. New Ser. vol. iv. 

 p. 318. 



3 Harlan, < Med. and Phys. Research.' p. 254. * Hays, loc. cit.'p. 317-337. 



