Shell very large, up to 110 mm. (4,37 inches) in length, very solid, narrowly-ovate, and frequently high in profile, the apex at about the anterior third.

Radial ribbing coarse and irregular in size; juveniles with about 22 primary ribs, increasing by interpolation to about 50 primaries in the adult, and there are finer subsidiary radials in the interstices. Interior porcellanous, with the crenulated border variably maculated, and with a well-defined, very large spatula, mainly white, or diffused with yellowish brown, but often surrounded at its outer edge by an irregular zone of deep orange-brown.

The margin is rather wide in young shells but relatively narrow in the fully adult, and bears numerous radiate lines or thick dashes, in dark-brown, on a whitish ground. Externally the shell is usually eroded to a dull greenish grey, and sometimes bears one or two specimens of the acmaeid,