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Genus Mediolus

Shell is ovoid to subspherical to spheroid; circular in cross-section, about the vertical aperture through the fundus; shell wall comprised of agglutinating particles variously composed of xenogenous mineral grains and/or organic material derived from the ambient environment; agglutinating particles attached together with an organic cement; circular aperture characterized by thin collar of secreted cement with variable number of inward-oriented angular crenulations also composed of cement; delicate spines may be present, spines long and narrow, hollow, and composed of very fine agglutinating particles. Ecology: freshwater. Type species: Mediolus corona (Wallich, 1864)