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The Allotrioceratidae is a family of Middle Ordovician fossils, established by Rousseau Flower, 1955, originally including ''Allotrioceras'' and ''Mirabilocras'', assigned inferentially to the Endocerida and known only from structures interpreted as siphuncles. Later ''Williamsoceras'', ''Cacheoceras'', and ''Perkinsoceras'' (Flower 1968, 1976) were added. Similar ''Allotrioceras'' and ''Mirabiloceras'', known only from the Chazyan (upper lower MIddle Ordovician) of New York, are tubular organisms with complex interiors somewhat resembling that of the Endocerida. The later added ''Williamsoceras'', ''Cacheoceras'', and ''Perkinsoceras'' are true endocerids as indicated by their cylindroid shells, phragmocones, and siphuncles. ''Williamsoceras'' and ''Cacheoceras'' are from the Whiterockian stage (lower lower Middle Ordovian) of Utah. ''Perkinsoceras'', which appeared somewhat later, is from the Chazyan of New York, like ''Allotrioceras'' and ''Mirabilioceras'' but rather distinct from either. The Allotrioceratidae of Rousseau Flower (Flower 1955) is defined on the basis a structure within the siphuncle, assumed or real, known as an infula that consists of a thin dark, arcuate or curved, line with dark spots interpreted as endosiphunclular tubules. ''Allotrioceras'' and ''Mirabilioceras'' also have internal subdividing structures that somewhat resemble the longitudinal processes found the siphuncles of some endocerids including ''Williamsoceras'', ''Cacheoceras'', and ''Perkinsoceras''. The holotypes of ''Allotrioceras'' and ''Mirabiloceras'' are housed in the collections of the New Mexico Museum of Natural History and Science in Albuquerque, New Mexico. ==''References''== *Rousseau H Flower, 1955. Status of Endoceroid Classification. Journal of Paleontology Vol 29, no 3, May, 1955. * __ 1968. Some Additional Whiterock Cephalopods. New Mexico Bureau of Mines & Mineral Resources, Mem 19, pt 2. * __ 1976. Some Whiterock and Chazy Endoceroids, New Mexico Bureau of Mines & Mineral Resources, Part II, Mem 28, 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「Allotrioceratidae」の詳細全文を読む スポンサード リンク
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