Cyclotella kohsakaensis Tanaka & Kobayasi, sp. nov. is described: It was taken from a silt stone sample in a Kohsaka Conglomerate Member. The age of the material is assumed to be from the Pliocene Era based on the plant fossils in the stratum. This new species is characterized by its smooth central zone without fultoportulae or rimoportulae but with undulation, and by the marginal fultoportulae and rimoportulae on the depressed ribs, and the stria composed of the same size areolae arranged in hexagonal array.
Attachment of theca' components, valves opposed and girdle bands intercalated if present, is examined by SEM within individual frustules of four species, all of which are new as well in genera. In the first two discoidal species devoid of girdle the opposite valves are thickened at the edges to an annular flange to which they firmly adhere: Trochosirella restricta with auricular flaps occluding rimoportulae on the mantle of arcuate, petridish-formed valves; Lomonycus rotatus furnished with stalked tubes for the marginal fultoportulae on the loculate valves. At brimmed edges in the third species the valves and bands are successively overlain by the adjacent component; Nephrodiscus sawamurae (=Coscinodiscus sawamurae Akiba), which carries a reniform cave on each valve. In the last taxon, Paleopandorus pergracilis superficially similar to species of Diploneis Ehr., the valve squeezes its terminal edge into a shallow groove parallel to the valve surfaces and cut into both ends of a single broad band without any overlapping of edges on the frustule. This unusual fashion of valve in attachment is discussed with regard to the Macdonald-Pfitzer rule.
The morphology, ecology and new occurrence in Japan of the three species, Cyclotella shanxiensis Xie Qi, Achnanthidium pyrenaicum (Hust. ) H. Kobayasi and A. latecepharum H. Kobayasi, are reported. These three species are found in less polluted upper sections of the rivers. The former first species is only found in the Inabe-gawa (Inabe River), the second species is found in the Inabe-gawa, and the Tama-gawa and the third species is found in the Inabe-gawa, Ara-kawa and the Shimantogawa.
The fine structure of Cyclotella rhomboideo-elliptica Skuja was examined using light and scanning electron microscopy. Plenty of frustules of this species which are described here were taken from a diatomite layer that was inserted in the Upper Nakanojo Lacustrine Deposit (Middle Pleistocene) which is assumed to be from about 0.3 to 0.5million years old, middle Pleistocene, Central Japan. This species is characterized strongly by its asymmetrically distorted frustules. The frustules are parallelogram-shaped in the girdle view and from rhomboidal to elliptical in the valve view. The central part of the valve is externally reticulate-verrucose and prominently undulated.
Five new genera comprising eight new species are described from the Miocene marine sediment. Plurifenestra, composed of Plurifenestra cruciata sp. nov. and P. maxima sp. nov. as well as Unguiella typified by Unguiella grossecarinata sp. nov. with U. latispinifera sp. nov. is grouped into Plurifenestraceae fam. nov. on the basis of the common possession of large biserial window-like areolae on the mantle of discoidal valves. Siphonodiscus polysiphonius sp. nov. characterize radiating tubes which tunnel within the wall thickness of the lenticular valve. Rouxiopsis dependent upon Rouxiopsis bipartita sp. nov. has a reduced raphe as in the related genus Rouxia with sep arate slits on the apical sternum but with longitudinal rows of apparently closed areolae. In the final genus Balanosa composed of two new species, Balanosa fusiformis and B. continua, a large spindle-shaped chamber constitutes the longitudinal halves of the valve face. The reconstructed image of the fragment-based members of Plurifenestrace a e and the morphologic relationships for Rouxiopsis are discussed.