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''Perkinsoceras''is an endocerid genus from the Middle Ordovician (Chazyan) of Champlain Valley established by Flower in 1976, which he added to his Allotrioceratidae based on certain similarities to ''Williamsoceras'' and ''Cacheoceras'' which had been added previously. ''Perkinsoceras'' is characterized by a large ventral siphuncle in broad contact with the ventral margin of the phragmocone -the chambered portion of the shell- which is expanded into a Nanno type apex, and by a broad longitudinal ventral process about which the endocones are draped. ''Perkinsoceras'' has what have been interpreted as tubules that form where the endocones impinge on the process, a feature also interpreted in ''Williamsoceras'', ''Cacheoceras'' and the distinctly unique ''Allotrioceras'' ''Perkinsoceras'' differs from the generally similar ''Chazyoceras'' by its ventral process -absent in the latter, and by its more bulbous nanno type apex. ''Williamsoceras'' and ''Cacheoceras'' differ in having a straight cameroceras type apex without the expanded siphuncle. ''Allotrioceras'' differs by its vertical median partition separating the two lateral endocones. ''Perkinsoceras'' has a single set of endocones'' Two species of ''Perkinsoceras'' have been described, both early Middle Ordovician (Chazyan) in age, both from Vermont. ''P inflatum'' comes from the Crown Point Limestone, 1/2 mile south of Ferrisburg Vt. The holotype is in the Paleontology collection of the (New Mexico Museum of Natural History and Science ). ''P foerstei'' comes from Isle La Motte. Its holotype is at the U.S. National Museum in Washington D.C. ==See also== *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「Perkinsoceras」の詳細全文を読む スポンサード リンク
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