Quadrulella quadrigera  Deflandre, 1936

Diagnosis: shell colorless, ovoid or slightly pyriform, sides convex or straight; surface composed of quadrangular or sometimes circular, siliceous shell plates, which are usually arranged in a regular manner, usually in rows, with all plates more or less of the same size; aperture straight, surrounded by a thin collar of organic cement.

Dimensions: According to Deflandre (1936): Shell length 100–150 (174) μm; width 60–100 (120) μm.

Habitat: Sphagnum and moss.

Geographical distribution: North and South America, Asia, Russia, Australasia.

Quadrulella quadrigera var. africana Gauthier-Lièvre and Thomas, 1961

Gauthier-Lièvre and Thomas (1961): “We attach to this species a very abundant Quadrulella in two stations of the Middle Congo and which we had first identified with Q. symmetrica; it differs from the latter by its ovoid theca coated with square or rectangular plates, sometimes, but more rarely oval, smaller and more regularly arranged. One side shows platelets juxtaposed in regular oblique series, the other side also has oblique but often intersecting series and, at least in the part near the pseudostome, the platelets strongly encroach on each other; it is on this face that we observed the oval platelets.
The specimens from the Middle Congo differ sufficiently from the type in their narrow pseudostome to motivate the creation of a variety: var. africana var. nov.
Shell ovoid or subpyriform; main body broadly rounded, sides converging regularly towards a narrower pseudostome than in the type, truncated straight or very slightly convex, formed by a row of plates arranged like a straight collar with sometimes a thin chitinoid lip. Viewed laterally, the theca is claviform, compressed, with a non-indented pseudostome; the apical view is ellipsoid. Covered with square, rectangular plates, more rarely oval, transparent, of small dimensions.”