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Beekmanoceras
''Beekmanoceras'' is a small cephalopod from the Middle Canadian of New York with a loosely coiled, gyroconic, shell in which the whorls are not in contact and the siphuncle is on the inner or concave side of the whorl. Furnish and Glenister (1964) placed Beekmanoceras in the Trocholitidae (Tarphycerida), interpreting the curvature to be ventral side convex, i.e. exogastastric and the siphuncle to be dorsal. Flower (1964) included ''Beekmanoceras'' in the Ellesmeroceratidae believing the siphuncle to be ventral and the curvature to be endogastric with the vental side concave.
Structural details of the genotype ''Beekmanoceras priscum'' the only species known, are obscure, allowing for different interpretations (ibid). A few things can be said however. No other trocholitids are known to have an openly coiled gyroconic shell which casts doubt on that placement. On the other hand no endogastric forms are known for sure to have developed the kind of gyroconic coiling found in ''Beekmanoceras''.
== References ==
* Flower, Rousseau H, 1964; The Nautiloid Order Ellesmeroceratida (Cephalopoda); New Mexico Bureau of Mines and Mneral Resources, Mem 12, p.96
*Furnish, W.M & Glenister, Brian F.; Nautiloidea -- Tarphycerida, in the Treatise on Invertebrate Paleontology, Vol K, Teichert and Moore Eds, Pub GSA and Univ Kansas; p. K360.
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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