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Westonoceratidae are exogastric, mostly compressed, Discosorida of moderate size from the Middle Ordovician to the Lower Silurian. The siphuncle is typically close to the convexly curved outer margin of the phragmocone -the chambered part of the shell- taken to be ventral but may be more central in some genera. Connecting rings are thin to moderately thick with inflated bullettes grasping the preveous septal foremina. Parietal deposits within the siphuncle from endocones in advanced genera and cameral deposits are found in some. The Westonoceratidae are derived from the Cyrtogomphoceratidae through the cyrtogomphoceratid, ''Ulrichoceras''. In tern, the Westonoceratidae gave rise to a small group of discosorids, the Lowoceratidae, which form an intermediary step before the Discosoridae. Two principal lineages have been identified, both stemming from the genus ''Teichertoceras'', a derivative of ''Ulrichoceras''. One goes simply from ''Westonoceras'' to ''Winnipegoceras''. The other goes from ''Faberoceras'' to ''Clarkesvillia'' to ''Glyptodendron''. ''Faberoceras'' may also have given rise to ''Hecatoceras'' and ''Reedsoceras'' and is the likely source for the Lowoceratidae. Two other genera are included, but are separately derived from ''Ulrichoceras''. These are ''Sinclairoceras'' and ''Simardoceras''. ==''References''== * Teichert, Curt 1964. Nautiloidea - Discosorida; Treatise on Invertebrate Paleontology, Part K ; Geol Soc of America and University of Kansas Press * Flower, R H and Teichert, C; 1957. The Cephalopod Order Discosorida. University of Kansas Paleontological Contributions. Mollusca, Article 6, pp 1-144. 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「Westonoceratidae」の詳細全文を読む スポンサード リンク
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