Shell length to 480 mm; heavy, broadly fan-shaped; dorsal margin variable from straight to strongly convex; ventral margin broadly convex posteriorly, concave anteriorly, inflated. Sculpture: 10-17 major, often obsolete spinose radial ribs, crowded and more numerous on the ventral slope; posterior ribs usually bear large upright spines, open posteriorly. Colour: red-brown to black. Habitat: littoral sand and mud. Distribution: central Queensland to north Western Australia.