158 NEW-YORK FAUNA — MOLLUSCA. 
CREPIDULA PLANA. 
PLATE VII. FIG. 153. a. B. 
(STATE COLLECTION.) 
Crepidula plana. Say, Jour. Acad. Nat. Sc. Vol. 2, p. 226; Am. Conch. pl. 44. 
C. unguiformis? Lamarck, An. sans vert. Vol. 6, part 2. p. 25, Ed. prior. 
C. plana. Apams, Bost. Jour. Nat. Hist. Vol. 2, p. 276. 
C. id. Goutp, Invertebrata of Mass. p. 159, fig. 16. 
Description. Shell subovate or obscurely quadrilateral, depressed, very slightly convex, 
thin, polished, transversely wrinkled. Apex minute, pointed, forming a terminal angle, which 
in old shells is obsolete. Diaphragm convex, contracted in the middle and at one side, nearly 
half the length of the shell, rising nearly to a level with-the lateral margins of the shell; its 
free edge sinuous, and, according to Dr. Gould, in entire specimens has a deep notch on one 
side, and a more superficial one on the other. 
Color, white ; diaphragm satin-white. 
Length, 1:0-1°5. Width, 0°7 - 1:0. 
This is found on the seacoast of Long island, although more rare and generally much 
smaller than the preceding. It is parasitic on other shells, usually on the inner surface, where 
it is sometimes accompanied by the fornicata. Hence it has been regarded by some as a 
mere variety of that species, modified by its peculiar position. ‘The young are more orbicu- 
lar, and I have seen them strongly ribbed when taken from the pecten, as has been elsewhere 
remarked of Anomia. It is possible that a specimen, thus altered by position, may have 
given rise to the C. depressa of Say ; but it is proper to add, that I have never seen an au- 
thentic specimen of that species. It has a wide but less limited range than the fornicata, 
being found from Massachusetts to the Gulf of Mexico. 
CREPIDULA CONVEXA. 
PLATE VII. FIG. 131. 
Crepidula convera, Say, Jour. Acad. Nat. Sciences, Vol. 2, p. 227. 
Cc. id. Apams, Bost. Jour. Nat. Hist. Vol. 2, p. 279. 
Cc. id. Goutp, Invertebrata of Mass, p. 160, fig. 15, 
Description. Shell small, very ovate, convex, descending almost abruptly on one side, 
more gradually sloping on the other. Apex acute, separate from the body of the shell, and 
turning down nearly to the plane of the aperture and occasionally beyond it. Aperture oval- 
elongate. Diaphragm convex, less than half the length of the shell, deeply placed ; its edge 
waved or sinuous. Outer surface obsoletely wrinkled. 
