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''Subcollina'' is an evolute to serpenticonic stephanoceratacean ammonite from the Middle Jurassic (Baj) of Mexico, placed in the family Spiroceratidae.〔The Bajocian (Jurassic) ammonite fauna of Oaxaca, Mexico; Jose Sandoval & Gerd E. G. Westermann; Jour Paleo V.67, N.6, p.1220, Nov. 1986〕 The whorl section of ''Subcollina'' is subquadrate, slightly depressed in the inner whorls, slightly compressed at the mature aperture. The inner whorls are covered with fine, dense, primary ribs that become widespread and thicker on the outer whorls, terminating in ventrolateral tubercles from which two or sometimes three secondary ribs extend that cross the venter in a regular zig-zag pattern.〔 〔Mesozoic Ammonoidea, Arkell et al 1957.Treatise on Invertebrate Paleontology, Part L, mollusca 4〕 ''Subcollina'' is probably derived from the Stephanoceratidae.〔 Some stephanoceratids also have the zig-zag pattern of ''Subcollina''. Related genera include ''Parastrenoceras'', ''Strenoceras'', and ''Spiroceras''. Note that the described zig-zag pattern in the secondary ribs as they cross the venter may be hard to make out in fig 32 of Sandoval and Westermann (1986) ==''References''== 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「Subcollina」の詳細全文を読む スポンサード リンク
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