234 DESCRIPTION OF VERTEBRATE REMAINS, CHIEFLY 



Ag., from the eocene formation of Bracklesham, as represented in figure 14, PI. 

 xi., of Dixon's Geology of Sussex, England. The median teeth of the former are 

 proportionately not so wide fore and aft as in the latter. 



Myliobates mordax. 

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



Several specimens of the dental armature of Rays from the Ashley phosphate 

 beds, which have come under my observation, appear to indicate a species distinct 

 from the former, and also from M. Holmesii as characterized by the specimen 

 described by Dr. Gibbes. 



Two of the specimens pertain to the collection submitted to my examination 

 by Mr. J. M. Gliddon. One of them, represented in figure 1, PI. xxxiii., is an 

 inferior dental plate, and consists of the greater portion of nine median teeth 

 together with part of the first row of small teeth on one side. 



The triturating surface for the most part, nearly flat, is feebly curved fore and 

 aft, but is more convex transversely, and becomes more so approaching the lateral 

 borders. The surfaces of the median teeth successively incline slightly backward, 

 so that their anterior margins are decidedly elevated above the contiguous margins 

 of the teeth in advance. This arrangement produces an unusually uneven trans- 

 versely ridged surface like that often observed on the surface of an ordinary rasp. 

 The transverse sutures of the median teeth are nearly straight except at their 

 extremities where they curve backward. Feeble ridges, not laterally symmetrical 

 and interrupted by the prominent anterior margins of the median teeth, extend 

 along the dental pavement. 



The under surface of the dental plate slopes evenly from the median line to 

 the lateral borders. At the middle, the dental plate, including the root, is ten 

 lines thick. On the triturating surface, seven median teeth occupy an extent 

 fore and aft of 28 lines. The first of this series measures in the same direction 3| 

 lines ; the last of the series, 4 lines. The breadth of the median teeth in their 

 perfect condition has been about 88 lines. 



From the dental plate of Myliobates Holmesii, from the same locality, as 

 represented by Dr. Gibbes (Journ. Acad. Nat. Sc, 1850, PI. xlii., fig. 1), the 

 specimen just described difiers in a number of points. While it has nearly the 

 same breadth and thickness, thus indicating fishes of about the same size, the 

 triturating surface is decidedly less convex transversely, the median teeth are 

 proportionately of less width, and the transverse sutures are comparatively straight. 



