158 Fossil Gavialfrom New Jersey. 



destroyed all the superincumbent strata, excepting the more 

 compact iron sand-stone of the Navesink, and thrown them into 

 irretrievable confusion. 



For further details respecting this interesting region^ the 

 reader may consult Mitchill's edition of Cuvier, the papers of 

 Pierce and Morton in the 16th and 18th vols, of the American 

 Journal, and of Harlan, in the 4th vol. of the Journal of the 

 Academy of Nat. Sc. Phila. 



The entire collection consists of fragments of the jaw of a 

 saurian reptile ; a portion of a curious small jaw, upon which 

 I am unable to form a decided opinion ; and several vertebrae 

 of fish and reptiles. 



Dimensions of Fragment, fig. 7, plate III. or left Dental Bone. 



Length 4*1. Extreme breadth 1*5 nearly. 



Distance between sockets '8. 



Depth of sockets 1*5. 



Projection of tooth above the alveole 1*1. 



Transverse diam. of tooth above the socket '5. 



Longitud. diam. '6. 



Diameter within the socket '65. 



In order to understand the structure and arrangement of 

 these teeth, it may be necessary to recur to the process of den- 

 tition, as it exists among these animals. Their number never 

 varies with age ; and although they are formed by superim- 

 posed coats, yet their interior is always hollow. At the bottom 

 of the socket is to be found the replacing tooth, which gradu- 

 ally increasing, ascends into the hollow of the old tooth, presses 

 upon, and of course destroys, the pulpy nucleus within, which 

 has furnished nutriment to the old tooth. This latter tooth, of 

 course, easily falls out, is replaced by the new one, which, in 

 its turn, makes way for another; and this is often repeated 

 during the whole life-time of the animal. Hence, at any period, 

 if we examine the teeth of these animals we shall find always 



