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''Kionoceras'' is an extinct nautiloid cephalopod genus included in the orthocerid family Kionoceratidae with scattered worldwide distribution from the Middle Ordovician to the Lower Permian. Kionoceratids are orthocerids with prominent longitudinal ornamentation on their shells, sometimes augmented by secondary trasverse ornamenttion. Orthocerids are, of course, prehistoric nautiloides with generally straight and elongate shells, mostly with central or subcentral siphuncles. (Sweet 1964) ''Kionoceras'' is characterized by long, slender to rapidly expanding, shells with prominent longitudinal ribs separated by concave interspaces and, often, less conspicuous longitudinal and transverse lirae and striae. The siphuncle is central or subcentral, generally orthochoanitic; empty in Silurian type-species and in most from the Ordovician, but with annulosiphonate deposits in some from the Silurian and later. ''Kionoceras'' is found in North America, Europe, Asia, and Australia. The type-species ''Kionocers doricum'' comes from the Middle Silurian of Central Europe ==See also== * Nautiloid * * List of nautiloids 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「Kionoceras」の詳細全文を読む スポンサード リンク
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