150 



worn, and those of the fourth ridge very little. Both the sixth 

 and seventh teeth were slightly movable in their sockets. 



The tooth in front of the sixth deserves your attention, because 

 it presents the characters of the fifth tooth perfectly well marked, 

 and also because it is undergoing the process of exclusion, and 

 is ready to fall from its socket. This fifth tooth is very much 

 worn ; the cusps on the side, have, in a great degree, disappeared, 

 and instead of their irregularities, a smooth, lustrous surface 

 appears. So much was this tooth worn, that an absorption of its 

 fangs has already taken place, so that it is readily removable 

 from its socket, and exhibits a beautiful illustration of the pro- 

 cess which nature adopts in order to discharge the useless and 

 worn-out teeth. A portion of the anterior fang of this tooth 

 remains in its socket, corresponding with the fang of the tooth, 

 though both had their asperities removed by absorption. 



The jaw in front of this shows no trace of the fourth, or any 

 other tooth. The cavities of the three milk-teeth are entirely 

 filled, and a sharp ridge exists in their place ; the same is true 

 of the fourth tooth. So that, of the six original teeth, four have 

 disappeared, and two remain ; and to the two latter is added the 

 supernumerary. The anterior extremity of the left side, which 

 alone remains, presents the same appearances ; the three milk 

 molars, and the first permanent molar have disappeared, and a 

 portion of the socket of the fifth tooth only is visible. 



The jaw is pointed and wedge-like, and exhibits no appearance 

 of a mandibular tusk. 



I hope to have the opinion of the Society on the character of 

 this tooth. It is a new case in Mastodon giganteus^ and we have 

 to consider, whether it is a lusus naturce, such as is found some- 

 times to occur in the human body ; or whether it is an instance 

 of the power of the system to develop a new tooth in extreme 

 age, as in the case of the elephant spoken of by Corse ; or 

 whether it is the result of a law established by nature for the 

 development of additional teeth to a certain definite amount. 



Dr. A. A. Hayes read the following communication, on 

 the Saline Incrustations of the " Mauvaises Terres" of 

 Kansas : — 



