Genus Trigonopyxis Penard, 1912
Diagnosis: Shell brownish, hemispherical; aperture central, invaginated, frequently triangular but more often irregular, always surrounded by a ring of organic cement, with a second internal membranous wall. Nucleus ovular.
Five species. Type species: Trigonopyxis arcula (Leidy, 1879).
Ecology: Feeding on bacteria and fungi. Common in acid forest soil, litter, mosses (e.g. sphagnum).