40 Bulletin 5 310 



134 FOSSIL SHELLS. 



convex than the other ; the whole surface covered 

 with approximate, scaly striae : ribs elevated, round- 

 ed, with six or seven striae on the back of each ; 

 intervening grooves profound : ears equal : sinus 

 of the ear of the superior valve, not profound, 

 being barely one eighth part of the length of the 

 ear : withhi with broad rounded flattened ribs. 



Ivcngth five inches and three-tenths, breadth 

 five inches and seven-tenths. 



Specimens of this truly fine shell are not un- 

 common. The Academy has been long in pos- 

 session of several single valves, in an excellent 

 state of preservation, obtained by my friend Mr. 

 J. Gilliams, and others which were presented by 

 Mr. Watson, who purchased them at the sale of 

 the collection of the late Professor Barton. Mr. 

 Finch has succeeded in obtaining entire specimens 

 of the two valves of the same individual. I am 

 of the opinion that lyister's plate 167, is intended 

 to represent this shell, and that the singular ap- 

 pearance of the marginal striae in that figure is a 

 deviation from the ordinary formation of the spe- 

 cies, and is owing to the dislocation of the lines 

 of increment, and obliteration of the longitudinal 

 striae. Lister describes his specimens to be of a 

 "blue-clay colour," in this respect perfectly cor- 

 responding with two specimens before me. 



On one of the specimens is an imperfect AstrEA. 



2. P. Madisonius. Much compressed, with about 

 sixteen striated ribs. 



[J. A. N. S., Phila., ist Ser., Vol. IV, 1824.] 



