The Nut Shells 



The Finely-grooved Leda (L. ienui sulcata. Couth.) is 

 drawn out, narrowed, and sharply keeled behind the umbones; 

 it has a broad, rounded front. The surface is concentrically cut 

 with fine lines, obscured in life by a thin, green epidermis. Length, 

 I inch. 



Habitat. — New England northward, 



The Hooked Leda {L. hamata, Cpr.) a small flat shell, with 

 its narrow posterior portion curved upward, is a deep sea form 

 taken with a dredge near Santa Catalina Island. Its grooved 

 sides are chestnut brown. Length, J inch. 



T. taphria, Dall, short-snouted, grooved and thick like a 

 bean, i inch long, is found in San Pedro Bay. 



Genus YOLDIA, Morch 



Shell thin, equivalve, polished outside, pearly within; dor- 

 sal line ends in angle behind; front rounded; valves flat; mol- 

 lusks active; usually found in shallows of river mouths or lee 

 shores. 



Cooper's Yoldia (Y. Cooperi, Gabb) is a thin, close-ridged 

 shell, with the hinge pointing backward and the sharp tip of the 

 "tail" of the shell pointing upward. The comb-like hinge line 

 bears about twelve teeth in front and forty or more behind the 

 beaks. The ribs are concentric. This deep water species occurs 

 off the coast of California, and attains a length of two or three 

 inches. 



Y. Montereyensis, Dall, a thin species with green epider- 

 mis and about twenty hinge teeth on each valve, is dredged 

 from mud at the depth of half a mile in Monterey Bay. Length, 

 I J inches. 



The File Yoldia ( Y. limatula, Say) has a veritable file on 

 the hinge line of each valve. The inconspicuous beaks are cen- 

 tral ; the valve rounds in front, narrows behind, ending in a sharp 

 angle at the dorsal line. A glazed green epidermis covers the 

 smooth surface. 



The slender united siphon is thrust up into clear water 

 from the mollusk's normal station just below the surface of the 

 mud. The foot is extremely broad and highly developed as a bur- 

 rowing organ. The thick, wedge-shaped extremity is thrust 

 out obliquely at the front ventral margin, and when fully ex- 



382 



