173 



the third and fourth molars of the left side in situ : the crowns of each 

 of these teeth are divided into three transverse ridges : the bony palate 

 is flatter than in the Mastodon elephantoides or the Mammoth. 



From the tertiary beds of the Ohio. Hunterian. 



712. A cast of the lower jaw, wanting the ascending rami, of a young Mastodon 

 giganteus : it demonstrates the sockets of the two incisive tusks which 

 characterize the immature state of the gigantic individuals of the present 

 extinct genus : one of the tusks is retained in situ. The three anterior 

 molars and part of the socket of the fourth molar are exhibited on the left 

 side ; on the right side the second; third, and fourth molars are preserved 

 in situ, together with the remains of the socket of the first molar, which 

 has been shed. Some of the changes in the dentition of the Mastodon, 

 as the teeth are successively developed from before backwards, are well 

 illustrated in this specimen, and the analogy of the process to the more 

 remarkable changes in the dentition of the existing Proboscidian Pachy- 

 derms may be clearly traced. The first molar, for example, is very 

 small and simple, as compared with the succeeding teeth ; its crown 

 supports only two transverse eminences with a small internal and poste- 

 rior talon ; viewed detached it might be mistaken for a tooth of the 

 Tapir: the second molar has nearly double the size, hut differs in the 

 form of the crown, chiefly through the greater proportional development 

 of the posterior talon : the third molar, besides being quadruple the di- 

 mensions of the first, supports three transverse eminences, and a narrow 

 ridge at both the anterior and posterior parts of the base : each of the 

 transverse ridges is slightly divided by a median cleft into two mam miliary 

 eminences : the summits of both those of the anterior ridge and of the 

 outer one in the middle ridge have been abraded. The fourth molar 

 presents an increase of size, but not quite to the same degree, as com- 

 pared with the third molar : its crowu has the same shape and structure 

 as in the third molar ; only the first transverse eminence has emerged 

 from the bony socket, which is situated on the inner side of the base of 

 the coronoid process, a part of which is preserved on the right ramus. 



The original of this specimen is preserved in Peel's Museum, New 

 York, and was first described by Dr. Godman as a type of a new genus 



