Elongated cylindrical, posterior end with scissor-crossed extensions (see inset), inflated, umbones near (but not at) anterior end, solid, whitish with yellow-brown periostracum often with calcareous encrustation, smooth, weakly radially divided by broad rounded keel; interior iridescent yellow-brown with purplish tint, margin smooth; living bored into soft rock or dead coral. North Carolina to Florida, Bahamas, West Indies, Gulf of Mexico, Caribbean Central America, South America (to Venezuela), also eastern Pacific, western Europe. Length 30 mm (to 52 mm). Compare other Lithophaga species (L. antillarum and L. nigra do not have calcareous posterior extensions, whereas those of L. bisulcata do not cross scissorlike), and Coralliophaga coralliophaga, which is whiter and thicker shelled with heterodont hinge teeth.

Distribution: North Carolina to Texas; West Indies. Size: 12 to 50 mm (1/2 to 2 in). Description: Color tannish-yellow to light brown, interior iridescent purplish-brown; shape oblong, narrow with a projection at extreme poste- rior end; sculpture rough with commarginal growth lines; shell covered with calcareous deposits; ligament long, extends from umbo to curvature at dorsal margin; anterior adductor muscle scar long, narrow, and close to margin, ad- ductor muscle scars not impressed. Habitat: Typically bores into calcareous rock. In Texas found at FGB. Depth range 0 to 165 m (540 ft). Remarks: Recognized by the crossing of the acute, extreme posterior margins of the valves. See Turner and Boss (1962); Lipka (1974); Odé (1979b).