282 



NORTH-CAROLINA GEOLOGICAL SURVEY. 



Shell very large, ribs, ten, and wide, and longitudinally 

 marked by fine ridges, which are not squamose. This species 

 is sometimes between nine and ten inches wide, and seven or 

 eight inches long, and are often used in cooking oysters in 

 place of a frying pan. It is one of the characteristic fossils of 

 this miocene. 



p. MADISONIUS. (Fig. 200.) 



In the P. Madisonius, the ribs number about fifteen, and 

 they are ornamented with three squamose ridges each. There 

 is also an equal number between them ; they coalesce towards 

 the hinge. 



FIG. 200. 





FIG. 201. 



A. pecten, (fig. 201,) is quite com- 

 mon in North-Carolina, which I have 

 not been able to refer to its proper 

 species. It is one of the most com- 

 mon in the shell marl of the middle 

 part of the eastern counties. It has 

 ten prominent ribs, but they are or- 

 namented in a different style from 

 that which prevails in the young of 

 the P. Jeffersonius. 



