新生代の珪藻属 Cavitatus WILLIAMS, 1981 の改訂と層序学的に有効な 2 新種 C. lanceolatus および C. rectus の記載

概要

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An emended description of a fossil diatom genus Cavitatus is presented, because the original description (WILLIAMS, 1989) is based on observation of poorly preserved specimens and lacks such important morphologic features of this genus as its heterovalvate nature, and the presence of areolae and rimoportulae. It is suggested that Cavitatus is most close to the genus Thalassionema. Cavitatus is based on Synedra jouseana SHESHUKOVA (1962), and has been monospecific so far. Our study shows that the genus comprises at least six species; C. jouseanus (SHESHUKOVA) WILLIAMS, C. linearis (SHESHUKOVA) AKIBA et YANAGISAWA stat. et comb. nov., C. miocenicus (SCHRADER) AKIBA et YANAGISAWA comb. nov., C. exiguus YANAGISAWA et AKIBA sp. nov., C. lanceolatus AKIBA et HIRAMATSU sp. nov. and C. rectus AKIBA et HIRAMATSU sp. nov. The last two new species have significant biostratigraphic utilities in the Cenozoic of Japan, because the former is restricted to a short interval in the middle Miocene Denticulopsis lauta Zone (NPD4A) and latter is limited to the upper Oligocene through lower Miocene, an interval below the first occurrence of Thalassiosira fraga.
国立科学博物館の論文
1993-03-22