Thalassiosira Lacustris Guide
Credit: Pat Kociolek
  1. Valve faces tangentially undulate
  2. Striae coarse
  3. Several marginal fultoportulae present
  4. Single marginal rimoportula present

The valve face is tangentially undulate. Striae are coarse and organized into somewhat radial rows. A ring of marginal fultoportulae is present. A prominent rimoportula is present on the valve face, close to the margin.