Rapheless valve
The epitheca of Achnanthes, Cocconeis and related genera. It does not bear a axial area is usually present.

Radiate
Condition where striae are directed towards the centre of the valve. Cf. convergent.

See characters:
- Striae, orientation at valve centre

Raphe
Longitudinal slit or furrow found in many pennate diatoms, through which mucus, for motility, is extruded. Divided into two parts, arranged end-to-end with a gap at the centre.

See characters:
- Raphe

Rimoportulae
(plural) Tubes on the valve, connecting the diatom protoplast with the outside. Possibly used in secretion of mucilage. See also fultoportulae.

See characters:
- Rimoportulae
- Rimoportulae, position

Rimoportula
(sing) see above

Ringleiste
A thickening on the inside of the valve of Aulacoseira (p. ##). Associated with the sulcus.

Rostrate
Condition where end of valve is drawn out slightly but not inflated. Cf. capitate, apiculate.

See characters:
- If protracted, shape

Raphid
Bearing a