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Fordilla
''Fordilla'' is an extinct genus of early bivalves, one of two genera in the extinct family Fordillidae. The genus is known solely from Early Cambrian fossils found in North America, Greenland, Europe, the Middle East, and Asia.〔(The Paleobiology Database ''Fordilla'' entry ) accessed 4 January 2012〕 The genus currently contains three described species, ''Fordilla germanica'', ''Fordilla sibirica'', and the type species ''Fordilla troyensis''.〔〔
==Description==
''Fordilla'' are small bivalves with valves that are equal in size and suboval in shape. In size ''Fordilla'' specimens reach a total shell length of up to and a height of .〔 The shells are compressed laterally and the back edge is slightly broadened. The rear adductor is less developed and smaller than the front adductor, while the small pedal retractor muscle scar is positioned near the front adductor scar.〔 The valve hing is usually straight to slightly convexly curved and each valve will have at most one tooth present. The external surface of the shell occasionally show faint ribbing.〔 The inner shell layers of ''Fordilla'' species, as with the related genus ''Pojetaia'', consist of layers of carbonate which is akin to the laminar aragonite layer found in extant monoplacophora. The structuring is similar to shell layering found in the extinct genera ''Anabarella'' and ''Watsonella'' which is thought to suggest members of the phylum Mollusca developed nacre independently several times.〔 Due to the size and age of the fossil specimens, ''Fordilla'' are included as part of the Turkish Small shelly fauna.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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