Shell solid, oblong, slightly oblique, inequilateral, little inflated. Colour dull white, upon the beak pale yellow. Sculptured by about forty-five close, raised, radiating ribs, separated by deep interstices a quarter of their width. In the median area the rays are smaller and closer together than at the sides, while at the extremities they rapidly enlarge and rather recurve. Upon the rays are crowded small transverse lunate gemmules. Lunule sharply impressed, narrow, lanceolate. Ligament large, external. Hinge line short, straight, remainder of the margin evenly rounded. Internal margin sharply, finely crenulated. Length 14, breadth 12, diameter of conjoined valves 8 mm.

This species seems nearest to G. dilecta. Smith, but is distinguished from that and other members of the genus by more numerous ribs bearing closer packed grains.