R Nodosum Guide
Credit: Marina Potapova
  1. Striae slightly radiate
  2. Striae biseriate
  3. Small central area
  4. Linear-elliptic shape

Valves are linear-elliptical or elliptical with slightly drawn-out ends. The striae are slightly radiate throughout both valves and biseriate. The axial area is narrow. The central area is small, or absent. If present, it may be asymmetrical on the rapheless valve.