Planothidium Bipororum Guide2
  1. Valves lanceolate with capitate apices
  2. Valves 5.4-7.0 μm wide
  3. Rapheless valve with a cavum

Valves are lanceolate with capitate apices, 12-25 μm long, 5.4-7.0 μm wide. The rapheless valve has a linear-lanceolate axial area and an asymmetric central area containing a cavum on the internal valve surface. The striae are multiseriate and radiate throughout both valves, 12-15 in 10 μm.