Frustules slightly to moderately bent in girdle view with a raphe system only on one valve (monoraphid); linear, lanceolate or elliptical in valve view, with broadly rostrate or scarcely rostrate apices; girdle narrow, so that cells most often lie in valve view.
Frustules heterovalvar, isopolar, bilaterally symmetrical; bent in girdle view, with the raphe valve on the ‘inside’ of the bend; the raphe valve and pseudoraphe valve are differently patterned.
Striae uniseriate, radial (less so in the pseudoraphe valve), coarse in many species (relative to the small size of the valves in this genus); areolae circular to transapically elongate in the raphe valve, circular in the pseudoraphe valve; occluded by fine pore plates (hymenes).
Axial area narrow and linear, or broader and lanceolate. Central area not differentiated from the axial area in either type of valve.
Raphe straight, bordered externally by a narrow groove on either side; external central endings slightly expanded; internal central endings straight, coaxial; terminal fissures turned to the same side.
Girdle structure unknown.
A single chloroplast per cell, lying against one side of the girdle and one valve.