抄録
Approximately 380 valves of Fragilaria capucina var. gracilis were identified on the light photomicrographs from a sample collected from the small pool along Daiya-gawa River. The valves with capitate ends were rare and the margins of the valves gradually narrowed in many specimens (about 91%) from the center to the ends of the valve. According to the original illustration by Oestrup, the breadth of an axial area was wide, while it was narrower in our specimens (about 84%). The central area of our specimens were weakly developed in many valves (62%). The valve morphology of our specimens resembled the illustration of F. capucina var. gracilis by Hustedt (1950) more than the original illustration of F. gracilis var. gracilis by Oestrup (1910). In addition, the microphotographs of F. gracilis Oestrup, Lectotypes Coll. Oestrup 1342 (Tafel 110 Figs 9-11) by Krammer & Lange-Bertalot (1991) closely resembled the valve morphology of our specimens as well as the breadth of the valve.
