158 INVERTEBRATA OF MASSACHUSETTS. 



CREPIDULA FORNICATA. 



Shell oval, apex turned to one side, and terminating in the mar- 

 gin ; partition oppressed to one side. 



FIGURE 17. 



State Coll., No. 123. Soc. Cab., No. 817. 



Patella fornicata, LIN. ; Syst. Wat., 1257. MARTINI ; Conch., i. 160, t 13, f. 129, 



130. LISTER ; Conch., t. 545, f. 33, 35. KNORR ; Vergn., vi. t. 21, f. 3. 

 Crepidula fornicata, LAM. ; vii. 641. SAY; Journ. Acad. Nat. Sc., ii. 225. 



Shell obliquely- oval, one side more oblique than the other, 

 apex a little prominent, turned to one side, not separate from the 

 body of the shell, and generally united with the margin of the 

 aperture ; convexity moderate, but varying according to the ob- 

 ject on which it is seated ; surface wrinkled by the lines of 

 growth, of a dirty-white color, and figured with interrupted, 

 waved, longitudinal lines, of a light-chestnut color, and covered 

 with a yellowish epidermis ; aperture obliquely sub-oval, the edge 

 entire and sharp, color light-brown, with darker dots and blotches ; 

 a ray from the apex along the middle of the shell generally lighter 

 than the rest ; diaphragm white, occupying about one half the 

 aperture, one side of it defined by a distinct line, the other, for a 

 considerable space, compressed against the side of the shell, and 

 firmly united to it, the free edge waving, one half advancing con- 

 siderably beyond the other, and leaving a conspicuous notch at 

 the side, outside the boundary line,, surface in general concave, 

 but a narrow, arched portion traverses the middle. Length 1 \ 

 inch, breadth 1J inch. 



Found adhering to other shells and to each other. 



This is probably, what Mr. Say supposed it to be, a variety of C. 

 fornicata, as originally described, an.d is a species found in various 

 seas. It is found occasionally thrown upon the beaches near Boston 

 after a storm, but is not uncommon about Cape Cod, and the islands to 

 the southeastward. The best specimens I have seen, were brought, 

 on oysters, from Prince Edward's Island, off the mouth of the St. 

 Lawrence. Its shape varies according to the body on which it rests. 

 Four or five of different ages are frequently found riding upon each 



