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''Cyrtogomphoceras'' is a nautiloid cephalopod, recognized by its large breviconic shell with a notable endogastric curvature. The shell is fusiform in profile, reaching maximum width at or near the base of body chamber, which narrows toward the aperture. The siphuncle is large and slightly removed from the ventral side, that with the concave longitudinal profile. Siphuncle segments are short, as are chambers; septal necks recurved, connecting rings thick, bullettes at the apical end of the rings swollen. Cameral deposits are lacking. ''Cyrtogomphoceras'' seems to be derived from ''Strandoceras'' by a reduction in the degree of endogastric curvature and may have given rise to ''Landeroceras'' by a further evolutionary straightening of the shell. ''Cyrtogomphoceras'', named by Foeste, 1924, has been found in middle and upper Ordovician beds in North America and Greenland. Fossils identified as such have also been found in the Silurian of Estonia. The type species is ''Oncoceras magnun'' Whiteaves 1890. ==''References''== *Flower, Rousseau H. and Curt Teichert, 1957; The Cephalopod Order Discosorida, in University of Kansas Paleontological Contributions, Mollusca Article 6, pp 1-144 (plates, figs) July1, 1957. *Curt Teichert 1964. Nautiloidea-Discosorida; Treatise on Invertebrate Paleontology Part K, Endoceratoidea, Actinoceratoidea, Nautiloidea.. Geological Society of America. 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「Cyrtogomphoceras」の詳細全文を読む スポンサード リンク
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