CLASS PELECYPODA 



To this class belong the oysters, 

 clams, scallops, mussels, and similar or- 

 ganisms, usually with bilateral symmetry. 

 The shell is usually of two valves and man- 

 tle of two lobes. Many of these live bur- 

 ied in mud or sand but often are attached 

 to rocks, shells, sponges, or other for- 

 eign objects. 



The shell, in two parts, is often 

 externally held together with an elastic 

 hinge and internally bound by the strong 

 muscles which must be severed to entirely 

 separate the valves. It is a defensive 

 covering against enemies and irritation 

 from without. 



As will be noted from the descrip- 

 tions of the respective families there is 

 wide diversity in form, size and sculpture 

 which result from the nature of the envi- 

 ronment, external Influences and heredita- 

 ry traits. 



ORDER PRIONODESMACEA 



An ancient group which has retained 

 many early features through long periods of 

 Geologic time. Lobes of mantle generally 

 separated; shell nacreous and prismatic, 

 rarely porcellanous. 



Family Solemyldae 



Shell equivalve, elongated; epider- 

 mis heavy and shining, extending far be- 

 yond margin. 



GENDS SOLEMYA Lamarck 1818 



SOLEMYA BOREALIS Totten. 

 shell than S. velum. The 



Fig. 29a 



Solemya borealis 



2 inches 



A much larger 

 valves are less 

 convex, more 

 solid.; grayish- 

 blue or lead 

 colored interi- 

 or; fifteen or 

 twenty radiat- 

 ing lines upon 

 epidermis which 

 is of a brown 



or tan color; ends of lobes rolled back. 



It has been collected on Chelsea 

 Beach, Massachusetts and off the coast of 

 Maine. Length 2 inches. 



Fig. 29a 



Nova Scotia to Connecticut 



SOLEMYA VELUM Say (Awning Shell). Shell 

 extremely thin and fragile; epidermis pale 

 brown with radiating lines; interior pur- 

 plish white; cartilage support arched. 



The epidermis hanging over the 

 edge like a veil at once distinguishes It. 

 Length 1 inch. 



PI. 2, Fig. 3 



PI. 73, Fig. 3 



Nova Scotia to Florida 



Family Nuculidae 



Shell transverse; no area for lig- 

 ament between umbones; a straight series 

 of teeth on each side, making an angle at 

 a spoon-shaped pit which separates them. 



GENDS NUCULA Lamarck 1799 

 (Nut Shells) 



NUCULA PROXIMA Say. Near Nut. Shell 

 small, thick, solid, very oblique in shape; 

 anterior end perpendicular to base; sur- 

 face sculptured with minute radiating 

 lines; epidermis dark green; interior 

 pearly; margin of shell crenulated; twelve 

 teeth before, eighteen behind umbones. 

 Length 12 mm. or less. 



Often taken in stomachs of fish in 

 New England. Dredged abundantly in shal- 

 low water off Cape Romano, west Florida, 

 by the writer in August 1933. 



PI. 2, Fig. 1 



Nova Scotia to Charlotte Harbor, 



Florida 



Family Nuculanldae (Ledidae ) 



Line of teeth interrupted by an 

 oblique pit for the ligament; most of the 

 teeth behind the pit; shell much produced 

 behind. 



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