FROM THE PHOSPHATE BEDS OF SOUTH CAROLINA. 2i1 



Figure 20 represents the left portion of a similar tooth of a larger individual, 

 presenting the same characters as the preceding specimen. The breadth of the 

 right side of the crown is 17 lines; its width at middle, 2| lines. The length of 

 the root is 5 lines. The breadth of the dental plate estimated from this tooth 

 fragment, is about two inches. 



Zygobates dubius. 



Leidy: Proceedings Academy Natural Sciences, 1855, 396. 



A species of eagle ray, with the dental organs tessellated in the manner of the 

 recent Zygohates Jussieu, was formerly indicated under the above name from a 

 number of isolated teeth, obtained from the Ashley River deposits by Capt. A. H. 

 Bowman. Similar isolated teeth are occasionally noticed among the collections, of 

 fossils from the more recent explorations of the phosphate beds of the same locality. 



Figures 21-37, Plate xxxi., represent teeth of the kind to which we allude. 



A median unworn tooth, represented in figures 21, 22, in form and size is 

 nearly like the more posterior unworn median teeth of the living Zygohates Jus- 

 sieu. It is straight transversely, but slightly bent, so that the triturating surflice 

 is a little concave from side to side. The triturating surface is feebly convex fore 

 and aft, highly polished, and slightly wrinkled longitudinally. The breadth of the 

 crown between the rectangular ends is an inch and a half; the width fore and aft 

 one fourth of an inch, and the thickness both at the middle and sides is three and 

 a quarter lines. The root of the tooth is lost. 



A second specimen of a median unworn tooth, represented in figure 23, resem- 

 bles the preceding, but is not bent in the same manner. Its measurements are as 

 follow: breadth, Y^ lines; width, 2| lines; thickness, 4| lines; thickness of 

 crown, 3f lines. 



A third specimen represented in figures 24, 25, is different enough in character 

 to pertain to another species. In its greater proportionate width fore and aft, in 

 the dull aspect and evenness of its triturating surface, and in the comparative thin- 

 ness of its crown, it resembles the more anterior worn teeth of the existing Zygo- 

 bates Jussieu in relation with the posterior unworn teeth. It is well arched with 

 the triturating surface convex transversely, instead of being nearly flat or slightly 

 concave as in the former specimens. Its measurements are as follow: breadth, 16 

 lines ; fore and aft width, 4 lines ; thickness, 3 lines ; thickness of the crown, 2 

 lines. 



A fourth specimen, represented in figures 26, 27, is like the last, but is of much 

 less width fore and aft. Its measurements are as follow: breadth, 16 lines; fore 



