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Nybyoceras
''Nybyoceras'' is an actinocerid genus assigned to the Armenoceratidae and similar to ''Armenoceras'' except for having a siphuncle close to the ventral side of the shell.
==Morphology==
As with ''Armenoceras'', ''Nybyoceras'' has a medium to large, straight shell.(Teichert 1964) Its primary diagnostic feature is its ventral siphuncle which the septa across obliquely.(Flower 1957,Teichert 1964) Ventrally, the septal necks are short and free, or recumbent for a short distance. Dorsally the brims are definitely recumbent.(Flower 1957) The connecting rings are broadly adnate to the septa ventrally at the posterior ends of the segments and dorsally at the anterior (adoral) ends.(Teichert 1964) Flower (1957) described the canal system within the siphuncle as being primarily of the single arc type, like ''Armenoceras'', and with interconnecing tubes. Teichert (1964) describes the canal system as being reticulate to curved and branching.
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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