Tomonori Naya

LANCINEIS RECTILATUS SP. NOV., A NEW FOSSIL SPECIES FROM PLEISTOCENE SEDIMENTS IN JAPAN

A fossil diatom species, Lancineis rectilatus sp. nov., is described from Pleistocene marine sediments of the Kanto Plain, central Japan. Lancineis rectilatus is characterized by (1) uniqueness of occurrence in geological time from the Pleistocene, (2) linear outline, (3) angular inflection of the valve outline, (4) a barely distinguishable narrow hyaline axial area and (5) orientation of a slit of rimoportulae orientated nearly parallel to the transapical axis at both apices. The new species is compared with other Lanceineis species, and the need to investigate valve ultrastructure of other Lancineis species is suggested. The stratigraphic occurrence of L. rectilatus indicates it is a possible stratigraphic marker useful for Pleistocene shallow marine sediments.

Marine Thalassiosira species from coastal Pleistocene sediments in central Kanto Plain, Japan

Nineteen species of the diatom genus Thalassiosira Cleve, including two tentatively identified and three unidentified species, are recorded from two sediment cores, drilled in Pleistocene coastal sediments of the Kanto Plain, central Japan. Concise descriptions obtained from the light and scanning electron microscopes are provided for the 19 Thalassiosira taxa recorded. This is the first study systematically investigating the taxonomy of the genus Thalassiosira and detailing the stratigraphic distribution of each taxon from Pleistocene coastal sediments of Japan. The species diversity of the genus Thalassiosira in the Japanese Pleistocene coastal environment is as high as in recent coastal waters.