The valve of this taxon is lanceolate to elliptical-lanceolate and the ends are obtuse and slightly protracted. The axial area is narrow and slightly widens toward the center area. The central area is transverse and irregular in shape. The striae are radiate and irregular in length (Patrick and Reimer 1966).
Pinnularia gastrum Ehr., Phys. Abh. Akad. Wiss. Berlin, for 1841:421, pl. 3(7), fig. 23. 1843 (Patrick and Reimer 1966).