Sellaphora subbacillum guide
  1. Valves linear to linear-elliptic with rounded apices
  2. Central area small, circular
  3. Striae radiate

Valves are broadly linear to linear-elliptic in outline. The central area is small, circular, and almost absent in some specimens. Striae are radiate. Grooves and conopea are present, but are difficult to resolve in LM.