Frustules distinctly cuneate (wedged-shaped) or gently linear, forming radiate colonies.
Valves heterovalvate and heteropolar, usually cuneate (wedge-shaped); valves with round, sometimes capitate, headpole, narrower footpole usually rounded.
Sternum narrow, sometimes valve edge has marginal solid spines.
Mono-raphid. Valve with raphe, extending ½ to ¼ of the valve face, terminating in helictoglossa; second valve with rudimentary or absent raphe.
Rimoportula present on raphid valve, as simple pore with paired lips.
Striae parallel, uniseriate; mantle margin sometimes with small plaques.
Girdle bands open, interleaved adjacent to one another in the series; valvocopula wider than copulae, usually with single row of pores; subsequent copulae decrease in size, overlapping someway before poles.