Valves linear-lanceolate, rhombic-lanceolate, elliptical to almost round, with broadly rounded to protracted ends; girdle narrowly rectangular.
Valves isopolar, bilaterally symmetrical.
Striae radiate, uniseriate, fine, areolae sometimes transversely elongated. Areolae occluded internally by hymens which, within a striae, can be confluent forming a strip on the inside of each stria.
Raphe central, stopping short of the apices, raphe sternum internally slightly thickened. Externally central fissures expanded, distal terminal fissures absent or deflected in opposite directions. Internally central fissures straight, unexpanded.
Valve face flat, curving fairly abruptly into shallow margins.
Girdle composed of narrow bands with transverse rows of small pores.
One or two chloroplasts, usually H-shaped in girdle view, comprising lobed plates under the valves, connected by a bridge containing the pyrenoid.