(Bosc, 1802)
Diagnosis: Shell distinctly curved dorsally, pyramid-shaped, transparent, triangular in outline and in cross-section. Elongated dorsal and lateral gutter shaped ribs enhance this shape. Greatest width of shell between tips of spines, at or behind middle. Ventral surface regularly convex, ventral rib appears as small swelling in middle disappearing near the shell aperture. Two latero-dorsal sides, delimited by dorsal rib, each with two inconspicuous ribs. Growth lines prominent, lateral sides rounded in cross section. At aperture, dorsal side of shell protruding above ventral side. Embryonic shell in adults spherical with blunt cusp, sharp cusp at tip of embryonic shell in juveniles. Constriction separates protoconch I from II, the latter cylindrical over whole length. Shell length 20 mm, width 30 mm.
Hydroids of Campaniclava cleodora (Gegenbaur, 1854) are sometimes found on the shell of this species.