Description. - Shell thin, translucent or subtranslucent, higher than wide. Right valve slightly more convex than left one. Ribs absent or present. Anterior auricles larger than posterior ones. Microsculpture consisting of very fine radiating grooves, which continues on the auricles between ribs. Byssal notch rather narrow, as well as ctenolium. Resilium triangular and relatively small. Shells vividly coloured.
Remarks. - The species of this genus have been erroneously classified in the genus Camptonectes Agassiz in Meek, 1864. Camptonectes, however, is an extinct genus, that inhabited the seas from lower Jurassic (Upper Lias) to upper Cretaceous (Maastrichtien) times. Palliolum originates in the Tertiary (upper Eocene).