Frustulia amphipleuroides

Valves are linear-lanceolate-rhomboid. The apices are broadly rounded apices and slightly constricted. Across most of the valve, striae are parallel or sometimes slightly radiate. Striae are very slightly convergent at the apices. Striae are radiate at the apices. In the longitudinal direction, the areolae are partially organized giving the longitudinal striae a wavy appearance. Areolae are generally unorganized at the center of the valve and minimal amount of organization is present near the apices. Externally, the openings of the areolae are lanceolate in shape. Internally, the areolae are oval and occluded by hymenes. The raphe branches curve slightly and are enclosed by longitudinal ribs. A very robust and slightly curved porte-crayon is present where the longitudinal ribs and long, linear helictoglossa fuse. The central nodule is elongate and fuses with the longitudinal ribs, which appear to be interrupted at the central area, rather than constricted. External raphe ends are slightly dilated and accompanied by a small, round depression. The central area may have 0-4 isolated poroids. An isolated poroid may also be present near the distal raphe ends.