(Childern, 1823)
Shell transparent, straight except for posterior part, triangular in outline, cross section oval. Three conspicuous dorsal ribs present, middle one broadest. Ventral rib so broad that it covers nearly whole ventral side. Lateral ribs double, with flat lateral surface between each pair of ridges, which may be concave distally, gutter-shaped. Sculpture of concentric undulations produces wavy transverse striation. Embryonic shell subspherical with clear cusp which may be worn off in older specimens. Radula formula 1-1-1, sometimes (1)-1-1-1-(1). Shell length 30 mm, width 17 mm, aperture 1/2 or more of total shell length.
Sometimes hydroids of Campaniclava clionis Vanhöffen, 1910 attach to the shell.