Frustulia Capitata Guide
Credit: Carrie Graeff
  1. Longitudinal ribs complete, or nearly complete, on one side only
  2. Capitate to subcapitate apices
  3. External proximal raphe ends unilaterally deflected

The longitudinal ribs of F. capitata are complete only on the side of the valve, the same side to which the proximal raphe ends are deflected. The valves are linear-lanceolate with capitate to subcapitate apices. The external proximal raphe ends are unilaterally deflected.