Staurosirella leptostauron var. dubia

Valves are heavily silicified, lanceolate in larger specimens and elliptical in smaller specimens, 3.5-6.5 µm wide by 4-38 µm long. Valves demonstrate rostrate ends in larger specimens becoming rounded in smaller valves. Valve face flat, or slightly undulate due to raised costae. The valve face/mantle junction forms a sharp angle. The abvalvar edge of the mantle is parallel to the valve face/mantle junction. In girdle view, frustules are rectangular and form ribbon-like colonies, probably joined by linking spines. The colonies are attached to the substratum at one end by a frustule attached by a mucilage pad, or colonies may be planktonic. The axial area is lanceolate. The striae are distinct, composed of lineolae gradually decreasing in size from the valve face/mantle edge to both the central sternum and the valve mantle, 6-10 in 10 µm. The lineolae bear finely branched volae. Lineolae are long forming wide striae that have the appearance of punch holes on the valve. Striae vary from parallel in the central area to radiate toward the valve ends. Striae extend deeply into the valve mantle. Costae are wider than the striae. The spines are reduced to solid prominences, two on each costa, between the striae. Striae are present along the valve face edge, except at the apices. Well-developed, ocellulimbus type, apical pore fields with round poroids are present. Apical pore fields are located on the valve mantle. Rimoportula are absent. Scab-like structures, or blisters, are absent. Copulae, or girdle bands are open and do not bear perforations. Valvocopula are wider than other girdle elements and bear developed fimbriae (finger-like projections).