Abstract
The material examined was taken from the pond of Botanical Garden in Copenhagen. The morphological characteristics in almost 364 specimens were analyzed by light microphotographs. Valve is linear-lanceolate and varies from thickset to long and slim types. Length to valve lO-34μm, mode 18μm, breadth 4-8μm, mode 5.5μm striae 13-18 in 10μm, mode 16 at the center of the valve, 16-20 in 10μm, mode 17 at both ends. Although this taxon is concidered to be Navicuta radiosa var. tenella judging from these measurements and the shapes of valves, some characteristics are different from some descriptions. The remarkable different points are as follows. Only 37% of the valves have the striae which are alternately longer and shorter about the central area. Stria at the central area which is reaching to the central nodule represents only 5.3%. Rhombic central area represents 65% including horizontally elliptical or rounded ones. We also observe the curved hook-shaped central nodule which which Krammer·Lange-Bertarot (1985) has confirmed by electron microscopy. Therefore, these specimens are named Navicula radiosa var. tenella.
