THE LANTERN SHELLS Genus PERIPLOMA, Schum.
Shell oval, valves very unequal, left valve deeper, posterior end contracted; lining pearly; hinge with narrow, oblique spoon The Duck-bill Shells and Lantern Shells shaped process in each valve, usually a triangular ossicle between; siphons separate, long, slender. About a dozen species distrib uted on coasts of the western hemisphere.
The Silvery Lantern Shell (P. planiscula, Sby.) has a smooth, delicate white shell with a silvery lining. Its hinge is near the posterior end of the oblong valves which taper toward the rounded anterior end. Under each beak is a spoon-shaped, forward-turning internal hinge tooth. The left valve is flat, the right bulged. These are such fragile shells that waves which cast one on the beach usually ruin the shell as a specimen for the cabinet. Length, t to 2 inches.
Habitat. Southern California.
The Paper Lantern Shell (P_ papyracea, Say) is fragile, white and pearly, like its prototype on the west coast. It is rounded in outline, almost as broad as long, but tapering somewhat to the posterior end, the outline falling abruptly from the sub-cen tral beak. The lines of growth and the groove from the beak are well marked. The surface is covered with minute wrinkles. The tooth is long, narrow, with an accessory process at the base. Length, f inch.
Habitat. Gulf of Mexico, Atlantic Coast. (Rare.) Lea's Lantern Shell (P- Leana, Conr.) has a broad, regu larly rounded outline, which slants away from the beak to the slightly narrow posterior end. I t is fragile and white, with a diago nal ridge from the beak. Surface wrinkled, with an overhanging yellow, shining epidermis. Each hinge has a spoon-shaped inter nal process set almost horizontally and resting on an oblique rib. Length, 14 inches.
Habitat. Northern Atlantic coast.
The Round Lantern Shell (P. discus, Strns.) is another of the fine species credited to the local collectors at Long Beach, Cal. For a time specimens were very rare. The valves are almost circular. The hinge line is approximately straight, and there is a truncated snout at the posterior dorsal corner. The thin, white valves are concentrically grooved. Length, 2 inches.
Habitat. San Pedro, Cal.
Genus LYONSIA, Turt.
Shell sub-triangular, valves unequal, thin; hinge with narrow ledge in each valve containing ossicle and ligament; siphons short, 328 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. Calif ornica, 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, 1 to t 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 3 inch.
Habitat. Whole Atlantic and Gulf coasts.
L. arenosa, Moll., is the size of a finger-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. curia, 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, 1 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, 1 inch. New England.
329 The Duck-bill Shells and Lantern Shells The Wavy Thracia (T. undulata, Conr.) is a rare species, larger and thinner than T. curia. The wrinkles are wavy on the posteria area. The general form of the valves is circular, with central umbones. It is found on the west coast.