Fani. 24.] NATUKAL HISTORY SOCIETY. 105 



dinal teeth usually two to three in each valve. Animal with a 

 very large and powerful foot ; siphons short and united ; gills 

 narrow. 



* Very elongated shells, over 4 times as long as high / . Ensis. 



* Not 4 times as long as high 2. Siliqua. 



1. Ensis, Schum. 

 Shell very long, subcylindrical, straight or slightly curved, mar- 

 gins parallel ; ends gaping ; umbones nearly terminal ; hinge teeth 

 one in each valve ; ligament long, external ; pallial sinus short 

 and square. 



1. Ensis viridis, Say. Shell smooth, 5 times as long as high ; 

 hinge margin nearly straight ; basal margin slightly curved ; an- 

 terior end somewhat truncate, posterior rounded ; hinge with 

 one tooth in each valve. Epidermis light green, glossy. L. 50 ; 

 H. 10 ; W. 6 ; U. i^. — New Jersey and south. 



2. Ensis Americanus, Gld. Shell smooth, 6 times as long as 

 high ; edges parallel and curved downward ; both ends some- 

 what truncate; right valve with one projecting cross tooth at 

 anterior end, and a longitudinal, ridge-like tooth extending 10 

 mm. towards the other end ; left valve with two cross teeth 10 

 mm.apart, and a double ridge between them. Epidermis glossy 

 greenish-olive, the long triangular space faded purple. L. 150 • 

 H. 25; W. 16; U. rV. — Whole coasi. Common, near low water 

 mark, in sand. 



2. Siliqua, Mege. 



Shell oblong, smooth, with a polished epidermis, and a rib 

 extending from the umbo across the shell on the interior surface. 



1. Siliqua costata, Say. Shell thin, fragile, smooth, oblong-oval, 

 with a rib-like, white ridge, extending from the umbo nearly 

 across the inside of the shell. Epidermis polished, violaceous 

 near the umbones, shading into olive at the margins ; the violet 

 more or less in triangular areas. L. 45 ; H. 18 ; W, 7 ; U. J. — 

 New Jersey and north. Common in many localities. 

 Family 24. MACTRID/E. 



Shell equivalve, trigonal, closed or slightly gaping, with an 

 internal cartilage contained in a deep, triangular pit ; two diverg- 

 ing cardinal teeth ; pallial sinus usually short, rounded. 



Animal with mantle quite widely open ; siphonal tubes joined 

 and with fringed openings. 



