134: DISTINCTION INTO SPECIES. 



Mastodon An examination of sixteen jaws shows mandibular tusks or vestiges of 



Tetracau- 



lodon. these tusks in nine instances, and an absence of them in seven ; thus 

 making the number of each not very different ; — a fact which, as far as it 

 goes, tends to prove that the Tetracaulodon was quite as likely to have been 

 the original type, as to have been a different species or variety of the 

 Mastodon Giganteus. 



Other circumstances alleged in favor of the specific Tetracaulodon 

 character are derived from the length of the rostrated or anterior portion of 

 the lower jaw, as appears by the following quotation from Dr. Godman's 

 description : — 



"The great • peculiarity of this jaw, and that which separates this 

 animal from every other genus hitherto established, is its elongated or 

 rostrated extremity, containing the alveolar processes or sockets for two 

 very remarkable tusks. The superior border of the jaw, from the situation 

 of the anterior teeth, declines immediately, tapering towards the level of 

 these sockets. Inferiority", the outline of the. jaw does not so immediately 

 change, until opposite, the anterior mental foramina, whence it suddenly 

 diminishes to the end. The rostrated portion of the jaw, anterior to the 

 front teeth, is three inches and three-fourths long, and superiorly is regu- 

 larly hollowed or grooved as for the reception of the tongue : this hollow is 

 two inches wide, quite smooth, and bounded on each side by thin raised 

 edges." 



On comparing a number of Tetracaulodon jaws with those of the 

 Mastodon Giganteus, we do not discover any difference of length in favor 

 of the former. But for greater exactness a comparison has been made of 

 a Tetracaulodon jaw with a Mastodon's of the same dimensions, by which 

 it appears that the length of the rostrated portion is seven inches and one- 



