P Scoticum Guide
Credit: Marina Potapova
  1. Valves linear-elliptical
  2. Rapheless valve with rhomboid axial area
  3. Striae radiate, 27-30 in 10 µm.

Valves are linear-elliptical. The raphe valve has a linear to linear-lanceolate axial area, which widens toward the center of the valve, and a transversely elliptical to rectangular central area. The raphe is straight, without terminal fissures. The rapheless valve has a rhomboid axial area, which often sharply widens in the valve center. Striae are radiate on both valves, 27-30 in 10 µm.