Abstract
Three new diatom species are described under the new genus Tropidosiphonus, separable from those hitherto assigned to Mediaria Sheshukova-Poretskaj a, which should now recur to the araphid category based on the lack of raphe system. They are Tropidosiphonus lanceolatus, T. secundus and T. tenuiconstrictus, all of which share a common appearance, bearing otherwise tubular endings. These internal tubes, termed helictosiphon characteristic of the new genus, is introduced from the evidence of SEM details as a new componental organelle of raphe system.
