Aperture usually surrounded by pores. Aperture diameter 0.45 of shell diameter. Shell diameter 70-160 µm.
Aperture surrounded by pores. Aperture diameter ≥ 0.4 of shell diameter. Shell very flat; diameter 140-402 µm.
Aperture surrounded by pores. Distinct basal rim. Height ca 1/3 of shell diameter.
Shell elliptical, quadrate or circular. Shell often with distinct dorsal folds or ribs. Aperture small and with pores.
