Frustulia Crassinervia Guide
Credit: Carrie Graeff
  1. Valve margins undulate
  2. Apices moderately protracted
  3. Porte-crayon small
  4. Longitudinal ribs slightly constricted at center

The valves of F. crassinervia are rhomboid in shape, with undulate margins and moderately protracted apices. The porte-crayon is small. At the valve center, the longitudinal ribs are constricted, but only slightly.