FROM THE PHOSPHATE BEDS OF SOUTH CAROLINA. 243 



be a fragment of the inferior dental pavement, and at its fore part is worn from the 

 attrition of food. It is especially remarkable for its thickness in relation with its 

 breadth ; the crowns of the teeth at the middle of the plate being 7| lines thick, 

 and thin away to a sharp edge at the lateral border, in a distance of an inch and 

 a quarter. 



The triturating surface is transversely convex and even. The median teeth 

 with their intermediate sutures are nearly straight, and curve backward but 

 slightly at their outer extremities. 



Apparent traces of a second row of small teeth are seen in the specimen external 

 to the more conspicuous teeth of the first row. 



The intermediate two median teeth of the specimen measure each fore and aft 

 5 lines. The breadth of the median teeth in a complete condition appears to have 

 been about 2^- inches. The thickness of the dental plate in the middle is 10 lines. 

 The inferior surface slopes with a slight inflection from the middle to the lateral 

 border. 



In the proportionate thickness and breadth of the dental plate and the con- 

 vexity of the triturating surface, it resembles that of Myliobates Holmem, but 

 the median teeth and transverse sutures differ in their comparative straight 

 course. 



Myliobates. 



Several fragments of dental plates, found with the preceding in Charles Co., 

 Md., may perhaps pertain to another species. One of the specimens, represented 

 in figure 7, PI. xxxii., consists of a portion from the back part of an inferior dental 

 pavement, comprising five median teeth with portions of one contiguous lateral 

 row. The triturating surface is nearly flat, being slightly convex transversely fore 

 and aft. The median teeth and their intervening sutures are more straight than 

 in any of the specimens previously described, except that referred to M. serratus. 

 The transverse sutures, though generally nearly straight, are slightly irregular in 

 their course. In the specimen the first one bends a little forward towards the 

 middle; the second is the straightest of the series; the third and fourth are nearly 

 like the first. 



The inferior surface of the dental pavement slopes gently from the median line 

 towards the lateral borders. 



Thickness of the pavement at the middle 5 lines; probable breadth when entire 

 about 2| inches. Breadth of median teeth when entire about 28 lines; fore and 

 aft width of the same ranging from 4 to 5 lines. 



