Fam. 32.] NATURAL niSTORY SOCIETY. Ill 



valve projecting over the left, except at the sliorter eixl ; gener- 

 ally gaping; umboiies rather prominent; gonial and podial 

 ridges broad and wavelike, dividing the surfoce into three, tri- 

 angular, concave p)Ttioiis; surface coarsely wrinkled. Epider- 

 mis thin, dingy-yellow. This species is so variable in form that 

 no general descji])tion can be given. It has received, at least, 

 five generic and fifteen specific names. Common size, L. 25 ; 

 H. 15; W. 10, U. J. Sometimes 60 long. Foot of animal 

 very slender, and bright orange-red. — Whole coast. Common, 

 especially north -of Cape Cod, from low water downward, on 

 ■weeds and timlxTS, and in sand, mnd and soft stone, 

 2. Cyhtodaria, Daud. 



Shell oblong- umbones hi\ck of centre; ligament large, on the 

 shorter end ; hinge thick, without teeth. 



Animal very large; mantle closed; siphons united in one 

 thick envelope. 



1. Cyrtodariu siliqua, Chem. Shell oblong-oval, solid, widely 

 gaping at both ends, without cardinal teeth ; umbones not promi- 

 nent, eroded ; ligament large on the shorter end ; interior covered 

 with a thick deposit of shelly substance with a fringed edge. 

 Epidermis thick, black, shining. L. 85 ; H. 35 ; W. 25 ; U. i— 

 Mass and north. Rare. 



Family 32. PHOLADID/E, 



Shell thin, white, brittle, hard and gaping at both ei-»ds ; armed 

 in front with rasp-like folds ; without hinge or ligament but 

 often furnished with extra valves; hinge plate reflected over the 

 umbones ; pallial sinus very deep. Animal club-shaped ; foot 

 short and truncated ] mantle closed in front except for the foot ; 

 siphons large and united nearly to the ends, which are fringed. 

 Living in rocks, wood or clay, 



* Small shells, 25 or less long S. Martesia. 



* Large shells, 40 or more long; surface covered by rough, radiating ridges, 

 at least on anterior end. (A.) 



A. Two or more times as long as high ; umbones connected by a broad, 



reflected hinge plate 1. Pholas. 



A. Not quite twice as long as liigh ; hinge plate only slightly reflected... 



2. ZirijhcBa. 



1. Pholas, L. 

 Shell elongated, cylindrical ; dorsal or hinge margin protected 



