Genus Pentagonia  Gauthier-Lièvre & Thomas, 1958

Diagnosis: Shell chitinoid, covered with mineral particles, polygonal in cross-section, more or less pyriform overall appearance. The irregular shape of the transverse section is due to longitudinal swellings which may end in a point towards the bottom of the theca. The circular pseudostome is surrounded by a slightly flared collar which tends to curl outwards; the opening of the pseudostome is small, while the diameter of the collarette manages to reach half the average diameter of the theca.

Ecology: Freshwater, sediments; Africa and Europa.