272 CALYPTR^ID^. 



ribs corresponding to those of the Pccten. It is a solid shell, and 

 the diaphragm is situated near the mouth, leaving no cavity extend- 

 ing under the beak. The manner in which one edge is pressed 

 against the side of the shell is quite characteristic. The margin of 

 the aperture is generally wliite, dotted with chestnut ; the remainder 

 of the interior is more or less brown. Sometimes the attachment 

 of the diaphragm is bordered with reddish brown. 



Whole coast of New England ( Stimpson) ; St. Simon's Isle, Ga. 

 (^Cooper^ ; mouth of Rio Grande (^Schoti). 



Crepidula plana. 



Fig. 16. 



Shell ovate, flat, white ; apex acute, terminal ; diaphragm convex. 



Crepidula plana, Say, Journ. Acad. Nat. Sc. ii. 226 (1822); Amer. Conch, pi. 44 ; ed. 



BiNNEY, 74. — Gould, Inv. 1st ed. 159, fig. 16. — De Kav, N. Y. Moll. 158, pi. 7, 



fig. 153. 

 Crepidula uugui/ormis, Stimpson, Check Lists, 4. 



Shell ovate, flat, or as often a little concave or convex, thin, trans- 

 parent, wdiite, wrinkled with concentric lines of growth ; apex mi- 

 nute, pointed, turning a little to one side, and con- 

 stituting the extreme termination of the shell ; the 

 other extremity broader, and regularly rounded ; in- 

 terior white, of a brilliant polish, and irridescent ; 

 diaphragm less than half the length of the shell, con- 

 vex, rising to a level with the margin, free edge for 

 the most part straight, but having a projecting angle 

 near one side. Length, one and one fourth inches ; 

  ^'"'^' breadth, nine tenths of an inch. 



Found in the aperture of other shells. 



This species has also been observed through a wide region, ^fr. 

 Say noted it as far south as Florida. It does not, however, frequent 

 localities north of us. It is still regarded by some as a variety of 

 the C. fornicata modified by its position. But the peculiarity of 

 form, coloration, diaphragm, and habit of living seem to render it 

 sufficiently distinct. When young, it is of a more rounded form, 

 but becomes elongated by age. It is otherwise very variable in 

 shape, conforming to the position it occupies in the throat of some 

 other shell. 



This is very likely to prove to be the C. mig-info?'mis, Lam. (Pa- 

 tella crepidula, Lin.) In this opinion I have the concurrence of Mr. 



