In this section
Valves are identical (neither has a raphe; i.e. the genus is araphid). Frustules rectangular in girdle view and boat shaped in valve view. Transverse internal ribs (costae) are prominent, visible in both valve view (as thick transverse bands) and girdle view (as obvious structures below the surface of each valve face). The cells of some species join to form filaments or zig-zagging chains. Chloroplasts numerous, discoidal, golden-brown.