Valves linear, linear-lanceolate, or lanceolate, narrowing to rounded or protracted rostrate or subcapitate ends. Frustules rectangular in girdle view.
Isopolar, isovalvar, bilaterally symmetrical.
Striae more or less parallel, broad, sometimes shortened, biseriate with round aroelae or consisting of a row of elongate, complex areolae. Areolae externally occluded by cribra. Striae separated internally by distinct ribs.
Axial area linear, narrow to wide.
At each pole a distinct apical pore field, the ocellulimbus, set below the valve surface. One or two rimoportulae present near valve ends.
Number of chloroplasts varies from two to many.
Frustules can form short ribbon-like or fan-like colonies.