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''Margarites helicinus'', common name the helicina margarite or spiral margarite, is a species of sea snail, a marine gastropod mollusk in the family Margaritidae. ''Margarites helicinus'' has been established by Phipps in 1774 and not by Fabricus in 1780 as Winchworth (1932), Sneli (1970) (and others) mention. Dall established in 1919 two varieties,〔(Dall (1919) Descriptions of new species of Mollusca from the North Pacific Ocean; Proceeding of the U.S. National Museum, vol. 56 (1920) )〕 but both have become synonyms of ''Margarites helicinus''. * ''Margarites helicinus'' var. ''elevatus'' Dall, 1919 * ''Margarites helicinus'' var. ''excavatus'' Dall, 1919 ==Description== The size of the shell varies between 3. mm and 11 mm. The umbilicate, thin shell has a depressed-conoidal shape. It is flesh-colored, with paler at periphery and below the suture, fading into corneous around the umbilicus. The surface is very bright, shining, polished, and smooth except for fine subobsolete concentric lines around the umbilicus. The spire is conoidal. The apex is minute but obtuse. The suture is impressed. The shell contains about 5 convex whorls, the last very rapidly widening, somewhat descending toward the aperture. The rounded aperture is oblique, angular above, nacreous inside. The pearly iridescence is often visible through the shell. The narrow umbilicus is profound. Its opening is regularly curved, not separated from the base by a carina.〔(Tryon (1889), Manual of Conchology XI, Academy of Natural Sciences, Philadelphia )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Margarites helicinus」の詳細全文を読む スポンサード リンク
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