FROM THE PHOSPHATE BEDS OF SOUTH CAROLINA. 255 



conical, with the anterior border trenchant and the posterior border obtuse. They 

 are slightly bent backward from near the base, and have a slight posterior barb- 

 like projection to the point. The largest specimen is more coarsely striate at the 

 base than in the smaller ones, and it also exhibits an excavation produced by the 

 encroachment of its successor. 



DiODON VETUS. 



Leidy : Proceediugs Acadeinj^ Natural Sciences, 1855, 397. 



Diodon antiquus, Leidy, Cope: Kerr's Report Geol. Survey of North Carolina, 18t5, Appendix 



31, Plate viii., fig. 6. 



Among the fossils of the Ashley phosphate beds there not unfrequently occur 

 specimens of the dental armature of a species of Diodon. The first specimens 

 brought to my notice were obtained by the late Capt. A. H. Bowman, U. S. A., in 

 sand dredged from the Ashley River, and were described in the Proceedings of 

 this Academy for 1855. As usual with the Ashley fossils, the remains of the 

 Diodon consist only of the hardest part of the skeletal structure — the dental 

 armature devoid of the osseous jaws. 



In the existing Striped Balloon-fish {Diodon maculo-striatus, Chilomyderus geo- 

 metricus), the exposed margins of the jaws are occupied with a dental armature 

 forming a crescentoid band composed of a multitude of small flattened denticles 

 co-ossified with one another and with the jaw. Within the position of the mar- 

 ginal dental armature there is a second, appearing as a large tubercle, composed 

 of broad laminar denticles arranged in two piles. These piles are co-ossified in 

 the median line and with the marginal dental armature in front, as well as with 

 the jaw itself, the whole together forming a solid mass. 



The fossils consist of the marginal and the internal or oral dental armatures 

 retained in conjunction, or separated, and frequently of the elements of the same 

 more or less isolated. The decomposing effect of the water to which the remains 

 were subjected, has rendered the structural elements of the dental armature more 

 distinct than in recent specimens. From among a number of the fossils two of the 

 most complete are represented in figures 15, 16, Plate xxxiv., and they consist of 

 the marginal dental armature still retained in conjunction with the interior or oral 



dental armature. 



In one of the specimens, figure 15fl, the oral dental tubercle is worn concavely 

 with the hollow directed backward; in the other, figure 16, it is worn convexly, 

 indicating that this was opposed to the former. A similar difference between the 

 oral dental tubercles of the upper and lower jaw is scarcely obvious in several 

 specimens of our common Striped Balloon-fish which I have examined. 



