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Comments are given on the classification of the Cretaceous heteromorphy ammonoid family Nostoceratidae. A new genus is proposed to accommodate a distinct group of species, which is similar to Turrilit...oides in the mode of coiling and ribbing but has the apertural part of the body-chamber facing obliquely upward. This is probably ancestral to Didymoceras and several other genera, occupying a fundamental stock in the. family in parallel with Hyphantoceras. Thus two major lines of descent may be distinguished in the Nostoceratidae.続きを見る
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