NATURAL SCIENCES OP PHILADELPHIA. 201 



the vicinity of Charleston, South Carolina. The specimen fully confirms the 

 view that the animal is a fish. 



The dentary bone, from its symphysis to where it articulated with the angu- 

 lar bone, judging partly from the bone itself and the impression of the remain- 

 der on the matrix, has been a little over six inches in length. Its depth at the 

 symphysis has been about two and a quarter inches. 



Twelve teeth have occupied the alveolar border in a space of four inches 

 and ten lines, and perhaps a couj)le more occupied the part broken away be- 

 hind. The teeth form an unbroken row, close together, and generally differ 

 but little in size, though those posteriorly are a little the smaller. 



The perfect crown of the teeth forms a nearly regular cone, the fore and aft 

 diameter of the base slightly exceeding the transverse. It is curved inwardly, 

 pointed, smooth, shining, and even, except at the base, where it is slightly 

 fluted, being most so in the anterior teeth, and more or less feebly so in the 

 hinder ones. 



The crown ceases at the alveolar margin, where it becomes continuous with 

 a more robust, solid, oval fang, which is inserted into the jaw and coossified 

 with its alveolus. 



In the dentary bone above mentioned, the crown of the first tooth, or that 

 nearest the symphj-sis, is broken off, displaying a clean continuous disk of vaso- 

 dentine, nearly circular, and about four lines in diameter. The fang is visible 

 from a destruction of a portion of the bone. It is half an inch long, of greater 

 diameter than the base of the crown, and composed of bone hardly more dense 

 than that of the jaw itself, with which it is coossified. The fourth tooth of the 

 series is in the same condition as the former. 



The crown of the second tooth had been shed, and its remaining solid fang 

 is somewhat encroached upon, through absorption, by the fang of the tooth 

 in front. 



The third, eighth and twelfth teeth have been shed, and their fangs absorbed, 

 leaving deep oval cavities. These were filled with matrix, and nothing more. 

 It is probable they contained successioual teeth, which dropped out in the 

 decomposition of the animal. 



The fifth tooth had been shed, and its remaining fang contains a funnel- 

 shaped pit. 



The sixth and tenth teeth alone remain in the specimen, the latter entire, 

 the former without its point. The crown of the sixth was nearly eight lines 

 long; the other is seven lines. 



The crown of the seventh tooth has been broken off, and the fractured surface 

 displays a small central cavity. 



The crown of the ninth tooth, which yas smaller than any of the others, is 

 shed, leaving the fang somewhat excavated; but the sides are narrowed, as if 

 the position of the tooth were to have been obliterated to give more room for 

 the accommodation of others. 



Back of the tenih tooth there is a small pit, probably the remains of the 

 position of an early tooth smaller than that last indicated. This incUided 

 would give thirteen to the series. 



The crown of the eleventh tooth had been shed, leaving a shallow basin on 

 the top of the fang. 



I could find no successioual teeth in the specimen. Those which existed 

 appear to have dropped out of the exposed cavities. 



From a study of the fragment it would appear as if the germs of new teeth 

 originated in the centre of the preexisting teeth, — that is, at the conjunction 

 of the crown and fang. In the development of the new tooth it was first 

 accommodated in its growth by the absorjition of the fang of the old tooth. 

 The crown of the latter being shed, that of the new one gradually assumed its 

 position, and when protruded its fang became coossified with its alveolus. 



A specimen in the museum of the Academy, from Ashley River, S. C, con- 

 sisting of an isolated tooth with the greater portion of its fang, is larger than 



1868.] 14 



f' 



