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''Bathmoceras'' is a primitive cephalopod genus from the Middle and Upper Ordovician, type for the family Bathmoceratidae, order Ellesmerocerida. Furnish and Glenister, 1964 include ''Eothinceras'' in the Bathmoceratidae along with ''Bathmoceras''. Flower, 1964, separates the two genera into their respective families which he included in his suborder, Cyrtoceritina The shells of ''Bathmoceras'' are rather large, straight or faintly exogastric. Sutures are simple except for a sharp mid ventral saddle. The siphuncle is large and near the venter, in which the segments have a slightly sinuous outline. Septal necks are rather long. Most diagnostically, the connecting rings are thickened into forward projecting lobes that may extend internally two or three segments within the siphuncle. Bathmoceras is of Middle and Late Ordovician age and has been found in northern and central Europe and in the Macdonnell Ranges in central Australia. At one time Bathmoceras was thought to have possibly given rise to Polydesmia, once thought to have been the ancestral actinocerid. Since then revision of actinocerid phylogeny and of Ordovician stratigraphy in east Asia have cast doubts on this hypothesis. ==Derivation== ''Bathmoceras'' is most likely derived from ''Eothinoceras'' through lengthening of the septal necks and of the inward projections of the connecting rings in a forward direction. ''Eothinoceras'' differs in that the septal necks are vestigial〔 rather than being somewhat long as in ''Bathmoceras'' and that the inward projections of the connecting rings point straight in rather than projecting forward. Both are straight shelled or slightly exogastric. Eothinoceras is also apparently more slender.〔 Furnish and Glenister also included ''Eothinceras'' in the family Bathmoceratidae. R.H. Flower separates the two genera into their respective families which he included in his suborder, Cyrtocerinina.〔 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「Bathmoceras」の詳細全文を読む スポンサード リンク
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