A guide to the morphology of the Diatom Frustule, Barber & Haworth 1981
The Diatom:Biology and Morphology of the Genera. Round et al.(1990)
Cells solitary, naviculoid, lying in valve or girdle view. Usually 4 girdle-appresssed plastids, one in each quadrant of the cell: occasionally 2 plastids lying against the epivalve. An exclusively freshwater, epipelic genus of very wide distribution but rarely abundant.
Elliptic to lanceolate, occasionally linear, outline sometimes gibbous or triundulate, isopolar and isobilateral. Ends rounded, apiculate, rostrate or capitate. Raphe central, usually fine and threadlike with often a slightly oblique slit. The polar raphe endings are characteristically forked externally into two long, straight terminal fissures, while the central external endings are frequently curved or deflected in opposite directions. Stria uniseriate, appearing as lines of round or transapically elongate pores and interrupted peripherally by a longitudinal line or series of lines. Axial area narrow, central area rounded or elliptic, occasionally an oblique fascia.
A very distinctive genus set apart by the combination of valve, plastid and raphe structure.