Shells medium-sized to large (diameter of base without attachments 65–128 mm; height of shell 48–70 mm), rather depressed to moderately high-spired, widely umbilicate, with wide peripheral flange (30-40% of total diameter at base) which is simple in some species or is digitate or divided into numerous long, hollow, narrow, parallel-sided spines. Ventral side of peripheral flange non-porcellanous. Foreign objects usually small to very small covering less than 30% of dorsal surface. ==Species==