Biremis Undulata Guide
  1. Valves with a central expansion
  2. Apices cuneate
  3. Striae coarse, with 3 dash-like areolae
  4. Longitudinal canal marginal

Valves with a large central expansion and weakly tri-undulate margins. Apices are cuneate. Striae are coarse and composed of three transapically elongate areolae. A marginal longitudinal canal connects outer two areolae of each stria.