Additional descriptions of the new diatoms from the Miocene Nabuto Formation, central Japan

Abstract

Five new genera are described from observations by SEM and they are all monotypic: (1)Streptommion torsivum represents a linear, twisted araphid with occelli of different sizes on each apical mantle; (2) Sagittula transversaria is also an araphid like Eunotogramma, carrying on the ventral mantle a distinctive wall organelle similar to a rimoportula; (3) Gyropandorus annulatus involves a naviculoid having the axial raphe reduced within the panduriform hoop of alveolar rows on the valve; (4) Apterosoma translucida, similar to a Plagiotropis in gross morphology, is characterized by a canal raphe system which lacks fibulae and helictoglossae; finally (5) Eupterotrum pulcherum bears a close resemblance to Entornoneis but differs in the framework of alar canal and by having the elaborate girdle bands.
Rimobulla is explained in detail as a new organelle within the mantle wall and is compared to the rimoportula.