Some New Diatoms from the Miocene Nabuto Formation, Central Japan

Abstract

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.