FROM THE PHOSPHATE BEDS OF SOUTH CAROLINA. 245 



loid layer turns abruptly upward at the end of the tooth for about one line. The 

 anterior border of the tooth is angularly convex the greater part of its extent, 

 but is feebly deflected in the opposite direction laterally. At the end it presents 

 a projection adapted to a crescentoid depression or socket of the contiguous tooth. 

 The posterior border, corresponding in its course with the anterior, presents a 

 narrow flange along the greater part of its length, and a crescentoid socket at the 

 end of the tooth, adapted to receive the projecting border of the contiguous tooth. 

 The thickness of the tooth at the middle is four lines, from which it thins off to 

 2| lines just within the rounded lateral border. The breadth of the tooth has 

 been about 2| inches; the width fore and aft is four lines. 



The tooth is nearly like the corresponding ones of jEtobatis irregularis, Ag., 

 from the eocene of Bracklesham, as represented in figure 7, tab. x., and figures 

 2-4, tab, xi. of Dixon's Geology of Sussex, England. It bears much less like- 

 ness to those of the specimen ascribed to the same species and represented in 

 figure 3, tab. 47 of the Poissons Fossiles. 



Jj]tobatis arcuatus. 



Agassiz: Poissons Fossiles. Gervais: Paleontologie Fran§aise, PI. 80, 1-3. Cope: Proceedings 

 Academy Natural Sciences, 186*7, 139. 



Numerous isolated teeth from the miocene formation of Charles River, Mary- 

 land, have been referred by Professor Cope to the above-named species, originally 

 described by Agassiz from specimens found in the miocene formation of Switzerland. 



The teeth, generally worn and in fragments, sometimes vary so much as to 

 render it uncertain whether to consider them as belonging to the upper or lower 

 series. They resemble in form those of the living ^tohatis tiarinari, but, unless 

 the difference is due to wearing, they appear to have proportionately thinner crowns 

 and longer roots. 



Figure 14, Plate xxxi., represents the left half of an inferior tooth. Its tritu- 

 rating surface is flat and slightly wider at the ends than at the middle. The front 

 and back borders are nearly parallel but slightly inflected, and are oblique at an 

 angle of about 45°. The outer end is rounded off rather more abruptly than in 

 A. narinari. The breadth of the fragment obliquely is 1| inches; the width ranges 

 from 2| to 3^ lines. The length of the root internally is half an inch. 



Figure 15 represents the median portion of an inferior tooth. The triturating 

 surface is wider than in the preceding specimen, and the angle formed by the con- 

 junction of the two sides is more prominent forward than it would appear to have 



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