Pinnularia Polyonca Guide
Credit: Loren Bahls
  1. Valves triundulate
  2. Apices capitate
  3. Axial area broad, lanceolate
  4. Central fascia

Valves are triundulate with the broadest portion in the middle. Apices are capitate. The axial area is broad and lanceolate, merging with a central transverse fascia.