Abstract
397 individuals were researched on material from Tane Pond, Tottori City. The various structures of frustule and their frequencies are shown in Table 1.These frequency show no great difference from those published before for frequency calculations based on microphotograph. Frustule lengths range from 43.5-58μm, width 10.5-14μm, with striae density from 6-8/10μm on the dorsal and 10/10μm on the ventral. These val-ues are also consistent with previous reports.
Distribution was analyzed based on previous records. This species ranges from Sumatra to Southern China, Korea and Japan, with wide distribution in Japan.
From the present research on the features of this species, it is clear that the raphe correspond to type 5 (Krammer Lamge-Bertalot 1986 p.691) .
The entire central area and one portion of the axial area are speckled. There is one isolated stigma on the ventral side central area, but without exception the areas between the two central striae are extended upward. There are no previouscases ofCymbellawith an isolated stigma having these upward extemding striae. As these features have not been seen inCymbellapreviously, it should be thought that this species represents a special group withinCymbella.
