Pseudostaurosira americana

Valves linear to elliptic, with cuneate to rounded ends. The central area is linear to lanceolate. The valve face connects sharply with the mantle. The abvalvar edge of the mantle is parallel to the valve face/mantle junction. In girdle view, frustules are rectangular. Cells often form short ribbon-like colonies, joined by linking spines. The axial area is narrow and linear or, less frequently, slightly lanceolate. Striae are distinctly punctate and composed of square to round areolae, decreasing in size from valve face/mantle junction to axial area. Striae are slightly alternate (referring to how striae from opposite margins "meet" at the central sternum). Areolae bear branched volae. Areolae on the valve mantle may bear flaps partially occluding the external areolar opening. The striae are interrupted at the valve face/mantle junction by spines. Costae are broader than the striae. Spines are flat, spatulate and solid. Spines are present along the valve face edge, except at the apices. Conspicuous scar-like depositions are present along abvalvar edge of valve mantle. Reduced apical pore fields with round poroids ocellulimbus type) are present at both valve ends. Pore fields are located at the junction between the valve face and mantle. Rimoportulae are absent. Copulae, or girdle bands, are open and do not bear perforations. Valvocopulae are wider than other girdle elements.