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''Allotrioceras'' is a tubular fossil from the Middle Ordovician of the state of New York, collected by Rousseau H. Flower; included by him in the Endocerida and placed in a new family, the Allotrioceratidae.〔Rousseau H. Flower, 1955 Status of Endoceroid classification. Journal of Paleontology |Vol29, no3, pp 329–371〕 ''Allotrioceras'' is characterized by a lateral pair of subequal conical structures, resembling the endocones of endocerids, separated by a straight partition that extends more than half way across from either the dorsal or ventral side, as perceived, and runs along the length. What remains is thought to represent a siphuncle, which ranges from about 8 millimeters (0.3 in) to about 15 millimeters (0.6 in) in diameter. On the basis of diagnosis, inclusion of ''Allotrioceras'' and the Allotrioceratidae, for which it is the type, in the endocerida seems at best tentative. Some endocerids, derived from the Proterocameroceratidae, ''Najaceras'', ''Cacheoceras'', and ''Williamsoceras'',〔Rousseau H. Flower 1976. Some Whiterock and Chazy Endoceroids, Part II Memoir 28 New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico〕 have a longitudinal dorsal or ventral process, or both about which the endocones are formed, which the partitian of Allotrioceras somewhat resembles. In the Chihliocreratidae, also derived from the Proterocameroceratidae,〔{Rousseau H. Flower 1958. Some Chazyan and Mohawkian Endoceratida, Journal of Paleontology Vol32, no3 pp 433-458 〕 the main endocones are flanked by two smaller endocones, one on each side, superficially resembling ''Allotrioceras. The holotype of ''Allotrioceras'', ''Allotrioceras bifercatum'' Flower 1955, rests in the collection of the New Mexico Museum of Natural History and Science in Albuquerque, New Mexico. ==References== * Curt Teichert 1964, Encoceratoidea, K160—__ in Vol K Treatise on Invertebrate Paleontology, Teichert C and Moore, R, C, eds, GSA and Univ Kansas Press. * Collections of the New Mexico Museum of Natural History and Science,Albuquerque, NM. 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「Allotrioceras」の詳細全文を読む スポンサード リンク
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