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Venericardia (Venericor) nipponica and V. (V.) mandaica were described by YOKOYAMA (1911) on the type specimens from the Yotsuyama Formation, the Eocene Manda Group in the Miike coal-field, Fukuoka Pr...efecture. On the occasion the former was distinguished from the latter by having its larger shell and more frequent occurrence. Venericardia (V.) mandaica is yielded also abundantly in the Kattachi Formation of the Manda Group, and some specimens of Venericardia having the intermediate characteristics of those species have been found out before now (i.e., TOMITA et al., 1992). The present paper tried paleontologically to reexamine YOKOYAMA's type specimens registered in the University of Tokyo for taxonomic discrimination. We also tried to verify statisticaly about 200 individuals of Venericardia from the Manda Group of Omuta and the Shikiyama Formation of the Shimoshima Group in the Shimosu Island of the Amakusa on the basis of biometrical methods. The syntypes of Venericardia (Venericor) nipponica and V. (V.) mandaica can be only discriminated by the difference of the relative size of shell, but this feature is not essential character to distinguished from each other. The samples of Omuta and Amakusa could not be discriminated on the basis of analysis of variation and relative growth of the collected samples. Taxonomic discrimination and analysis of variation and relative growth clearly show that the samples of Amakusa consist of a single species. Venericardia (V.) nipponica may be represent the gerontic form of "Venericardia (V.) mandaica" which shows a difinite trend in growth.続きを見る
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