The Duck-bill Shells and Lantern Shells 



almost united, fringed; foot tongue-shaped, with byssal groove. 

 Eighteen species, in all seas. 



The Californian Lyonsia (L. Calijornica, Conr.) is narrowly 

 oblong, with a straight hinge line, and prominent beaks nearer 

 the posterior, swollen end. The anterior end tapers to a thin, 

 crooked blade with a dorsal angle. The outer coat easily rubs 

 off, showing the pearly inner layer. Length, i to i^ inches. 



Habitat. — California. 



The Transparent Lyonsia (L. hyalina, Conr.) has its pellu- 

 cid shell prolonged backward and compressed; the beaks turn 

 forward, over the rounded end. Distinct lines radiate from the 

 beaks; these are crossed by concentric wrinkles. Length § inch. 



Habitat. — Whole Atlantic and Gulf coasts. 



L. arenosa, Moll., is the size of a fmger-nail, rounded at 

 both extremities. It often has a film of sand on its opaque 

 white surface. New England coast. 



Genus THRACIA, Blainv. 



Shell oblong, nearly equivalve, slightly compressed, drawn 

 out and gaping over the separate siphons; surface smooth or 

 minutely roughened, cartilage processes thick, external, with 

 crescent-shaped ossicle; mantle closed; foot tongue-like; gill single, 

 thick, plaited. Twenty species in northern and temperate seas. 



The Short Thracia {T. curta, Conr.) is but little longer than 

 broad, with fine wrinkles on the posterior areas of the valves. 

 The hinge ligament is external, teeth small, pallial sinus shallow. 

 Length, i to 2 inches. 



Habitat. — California. 



T. Conradi, Couth., is the giant of the genus, being as large 

 as Mya arenaria — as the palm of one's hand. Almost as broad 

 as long, the valves have sinuous margins, which fall away from the 

 almost central beaks to a rounded front, and a truncated angular 

 rear. A strong ridge sets apart the posterior area. The point 

 of the left beak fits into a socket in the right. This thin-shelled 

 mollusk occurs in deep water off the Massachusetts coast and north- 

 ward, and also on the New Jersey coast and at Cape Hatteras. 



T. synopsis, Beck, almost circular in outline, flat, its white 

 valves engraved with close elevated growth lines, lacks the hinge 

 cavity. Length, i inch. New England. 



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