中新統男体山火山角礫岩層産 Phanerolepida expansilabrum (KURODA)

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Miocene gastropod, Phanerolepida expansilabrum (KURODA) was collected from the Early Middle Miocene Nantaisan Volcanic Breccia (OTSUKI, 1975) in Ibaraki Prefecture with its operculum in life position. The species is characterized by its shagreen sculpture and slender form. Since no associated molluscan species with P. expansilabrum from the formation, other phanerolepid species from the Japanese formations as Miocene Bessho, Oidawara, Morozaki, Chichibumachi, Pliocene Shinzato, Tomiya, Nobori formations are associated with bathyal forms. However, the present occurrence of the species with operculum suggests that the formation mainly composed of andestic pyroclastics might have been deposited at the bathyal bottom in associated with andesite volcanic activity. Operculum of Phanerolepida expansilabrum is of paucispiral type (TAKI, 1950) with calcareous shell of Turbo type (COX, 1960), and very resembles that of modern species, P. transenna (WATSON) but slightly differs from these species of Pliocene Shinzato Formation, P. rehderi MACNEIL which has slightly elongated one. The Shinzato specimens are collected in isolated form and its variation of the external morphology was already mentioned earlier. The trend of morphological features and external sculptures from the Miocene to Recent is shown by the slender and rough sculpture in Miocene and swollen and fine sculpture in Recent. However, the morphological change of operculum of this genus through the geological age should be examined in future by more good materials.
日本貝類学会の論文
1980-04-30

中新統男体山火山角礫岩層産 Phanerolepida expansilabrum (KURODA)

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