Studies on the Genus Nephrolepidina in Japan

The Nephrolepidina assemblages from the Early Miocene formations in Japan were studied giving full account to their systematics, stratigraphic distribution, and paleozoogeography. The Nephrolepidina samples from Italy, Greece and Australia were studied in comparison with the Japanese Nephrolepidina. For the evaluation of their classification and evolution, the external and internal morphology of the shell was studied for interpretation of the species variation, the growth of the organism, and based upon these parameters, the specimens from each recognized population were investigated biometrically by statistical treatment. Three form groups were recognized in the phylogenetic development of the embryonic acceleration of the local Nephrolepidina populations ascertained in the respective areas studied. Based upon these groups the Early Miocene Series in Japan could be subdivided. Among the nephrolepidinas studied the following series of phylogenetic trends from the Chattian to Burdigalian, were recognized : Nephrolepidina. morgani-Nephrolepidina angulosa, Nephrolepidina tournoueri-Nephrolepidina howchini and Nephrolepidina tournoueri-Nephrolepidina japonica. Also included in this paper are the descriptions, geologic and geographic occurrences and phylogenetic trends of other larger Foraminifera genera as Miogypsina, Miolepidocyclina, Cycloclypeus, Homotrema and Gypsina which accompany Nephrolepidina in Japan