Abstract
The diatom flora in two samples, one collected in May 1970 from the lake center and the other in August 1991 from the southeastern shore of the Akan-ko (Lake Akan) were studied. The lake is one of the famous caldera lakes in Japan not only because of its beautiful scenery but also because it is the only place left in Japan to find the lake ball, Cladophora sauteri (NEES) KÜTZING. About 200 taxa were identified but here 16 centric taxa are reported with light and electron microscope photographs. Some comments are made mostly on the taxonomy of each taxon.
