Meridion Circulare Guide
Credit: Pat Kociolek
  1. Valves linear-clavate
  2. Costae present
  3. Narrow sternum
  4. Single rimoportula

Valves linear-clavate, asymmetric to the transapical axis. Costae are present running transversely across the valves. A narrow sternum extends the length of the valve. A single rimoportula is located near the headpole.