Planothidium Calcar Guide
Credit: Marina Potapova
  1. Valves elliptic
  2. Central area asymmetric
  3. Cavum present on both valves
  4. Central area reaches valve margins

Valves are elliptic. The axial area is narrow and linear on the raphe valve; the axial area is narrow and rhomboid on the rapheless valve. The central area on both valves is asymmetric, expanded to the valve margins and contains a cavum. The striae are fine and radiate throughout both valves.