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.
Shell elliptical, quadrate or circular. Shell often with distinct dorsal folds or ribs. Aperture small and with pores.
Shell with six or more ribs; dorsal surface with ribs and depressions; aperture smooth, without crenulations.
Shell in side view trapezoid, with six or more ribs; aperture smooth without crenulations.
Shell with basal border. Dorsal surface with depressions. Diameter c. 80-110 µm.
Shell in lateral view hemispherical, with acute or somewhat rounded corners, sometimes with a basal border. Diameter c. 35-55 µm.
Shell hemispherical, with smooth and broad rounded corners in lateral view.