FROM THE PHOSPHATE BEDS OF SOUTH CAROLINA. 233 



The specimen I have referred to a species and genus with the name heading 

 the present article. 



TBI ONYX. 

 I have repeatedly seen small fragments of the bony shell of species of Trionyx, 

 from the Ashley deposits, but too small to determine from them any important 

 specific character. Figure 3, PL xxxiv., represents a fragment of a costal plate, 

 one-half the natural size, apparently an eocene fossil from Ashley Eiver, presented 

 to the Academy by Mr. C. S. Bement. 



MYLIOBATES. 

 Myliobates maqtster. 

 Leidy: Proceedings Academy Natural Sciences, Ptiiladelphia, 1816, 86. 



A specimen of the dental armature of an eagle ray, in the Ashley collection of 

 fossils, indicates one of the largest of its kind. It is one-fourth larger than the 

 specimen from the same locality described and figured by Gibbes under the name 

 of M. Holmesii. It is not improbable that it may have pertained to a larger 

 individual of the same species, and its other differences may be accounted for by 

 supposing that it belonged to the opposite surface of the mouth. The original 

 specimen ascribed to M. Holmesii, judging from its convex triturating surface, 

 belonged to the roof of the mouth. The specimen under consideration may be 

 supposed to have belonged to the floor of the mouth. It is imperfect at the 

 extremities and lateral borders. Represented in figure 7, PI. xxxiii., the fore 

 part is deeply worn in evidence of the service performed by the organ in commi- 

 nuting hard food. The unworn surface is smooth, and is transversely convex, 

 but slightly depressed along the middle. Fore and aft it is in a less degree 



convex. 



The breadth of the median teeth is three and three-quarter inches, and five of 

 these teeth unworn occupy an antero-posterior extent of two and a half inches. 

 The sutural lines of the median teeth are slightly convex backward in the middle 

 and more strongly convex forward at the sides. 



The sutural lines of the median teeth are much less curved than is represented 

 to be the case in the specimen ascribed to M. Holmesii, but perhaps this difference 

 would exist between the upper and lower dental pavements of the species. 



The under or attached surface of the plate is too much broken away to deter- 

 mine the greatest thickness of the pavement. 



The specimen referred to 31. magister is about as large as that of M. Dixoni, 



