Diagnosis. Shell small, white, red-orange, or white with gray markings; sculpture of broadly spaced, imbricate radial ribs. Apex inclined anteriorly; protoconch erect, rounded, subspiral; apex of adult shell worn away. Interior termination of muscle scar posterior to apex. Animal with paired labial appendages. Fused inner lateral tooth of radula elongate and sharp pointed, outer pair of laterals greatly reduced and closely adjacent to fused inner laterals; marginal teeth narrow, inner surface with comblike fringe.
Remarks, Iothia differs from Lepeta Gray, 1847, in having an erect, non-spiral protoconch, the termination of the muscle scar behind the apex rather than in front of it, the marginal teeth narrower and fringed rather than smooth. The massive, sharp-pointed central tooth (a fusion of the inner lateral teeth) may function to pierce the tests of encrusting bryozoa, which often occurs on rocks bearing Iothia. Iothia species occur offshore, usually at depths greater than those accessible to divers.