FAMILY CALYPTRIADZ — CREPIDULA. 157 
GENUS CREPIDULA. Lamarck. 
Animal with its head convex, bordered in front with a bifid lip. Tentacles nearly cylindrical. 
large, obtuse, little contractile, with the eyes at their external base. Foot moderately thick, 
Mantle thin, without lateral appendices : branchial cavity very large, oblique from right to 
left, with a large opening; the gills form a transverse series of long filaments, which are 
capable of floating externally. Vent on the right in the same cavity. Shell oval, arched, 
cup-shaped, more or less elongated: spire imperfectly formed, and pressed against the 
margin. Cavity large, with trenchant margins, and partially divided by a horizontal par- 
tition. 
CREPIDULA FORNICATA. 
PLATE VII. FIG. 154, aputr; FIG. 152, rouna. 
(STATE COLLECTION.) 
Patella fornicata. Lin. Syst. Nat, 1257. 
Crepidula id. Lamarck, An. sans vert. Vol. 6, part 2, p. 42, Ed. prior. 
Cc. id. Say, Jour. Acad, Nat. Sc. Vol. 2, p. 225; Am. Conch. pl. 44. 
Cc, id. Gouxp, Invertebrata of Mass. p. 158, fig. 17. 
Description. Shell varying in convexity, with one side more oblique than the other: apex 
turned to one side, not separate from the body of the shell; surface transversely wrinkled. 
Partition or diaphragm smooth, slightly concave, occupying about half the length of the 
shell, with the margin uniting with the cavity in a solid manner; the free edge subacute, 
with a waving or sinuous margin. 
Color. Epidermis olive-green, tinged with light rufous, and with obsolete longitudinal un- 
dulated chesnut-colored lines: within reddish brown, the ends of the rufous lines appearing 
along the margin. 
Length, 1:0 —2°0. Width, 0°7-1°3. 
This species is the most common and the largest found on our coast. They are most usu- 
ally found adhering to each other, and to other shells; when adhering to the Pecten, the 
margin is observed to have undulations corresponding to the ribs of the Pecten. I have 
noticed four or five adhering to each other. It occurs from the mouth of the St. Lawrence, 
and probably further north, to the Gulf of Mexico. 
