Surirella Ovalis Guide
Credit: Jonathan English, Marina Potapova
  1. Keel low, alar wings absent
  2. Valves large, heteropolar
  3. Valve length 14-75 µm, width 11-35 µm
  4. Fibula density 5-6 in 10 µm
  5. Costa density 14-17 in 10 µm

Valves are extremely variable in size and outline, 14-75 µm long by 11-35 µm wide. The larger valves have cuneately rounded apices, while the smaller valves have two broadly rounded apices. Mid-sized specimens have one broadly rounded apex and one cuneately rounded apex. The costae number 14-17 in 10 µm and every third or fourth costa is raised above the others. The fibulae are marginal, 5-6 in 10 µm.