Nitzschia lacuum Lange-Bertalot, 1980

Figs 3AF-AW, 9

Notes.

The outline of the frustules is lanceolate with capitate to acutely rounded apices (Fig. 3AF-AW). Valves are 13-22 µm length and 2.0-3.5 µm in width. The ratio of length and width is 4.38-10.00. Striae 36-37 in 10 µm (undistinguished in LM). Fibulae are visible 11-18 in 10 µm . Striae are uniseriate, arranged transapically. Along the edge of the valve, where the raised raphe canal is located, two longitudinal rows of areolae are present (Fig. 9A, D) - a doublet nearer to the raphe and a single areola at the junction with the valve face opened to the interior of the raphe canal. Distal raphe endings are strongly hooked and deflect on each valve in different directions (Fig. 9A, B, D). The central nodule is absent (Fig. 9B). The proximal mantle possesses three rows of areolae (Fig. 9C). Valvocopula possess scalloped edges (opened pores) (Fig. 9C). The distal mantle is narrow and has scallops on the edge (Fig. 9B, C). Internally, fibulae have equal spacing, there is no wider gap between centre fibulae. Distal raphe fissures terminate with small helictoglossa (Fig. 9E).