Adult shell brightly glazed because exterior mantle protects it from damage and epizooic growths, and deposits fresh shell-material throughout life. Colours slightly faded after shell stored for 40 years.
1: scale line 11.2 mm, height of shell. Adult usually not less than 10 mm, and up to 13 mm.
2: columellar region a concave furrow; ribs protrude as teeth.
3: slight mound marking position of enveloped apex of spire. (Shell convolute, i.e. all earlier whorls hidden from view by enveloping final whorl.)
4: posterior dark, dorsal, pigment mark; usually largest of the three.
5: central dark, dorsal, pigment mark (faded on this specimen).
6: anterior dark, dorsal, pigment mark.
7: aperture a gently bowed slit along entire height of shell.
8: outer (palatal) lip of aperture curved out of sight into interior of shell.
9: wide extension of aperture at anterior forms inhalent siphonal canal.
10: extension of aperture at posterior forms exhalent siphonal canal.
11: about twenty strong, flat-topped ribs with intervening grooves. A few ribs do not extend across complete width of shell and some are misaligned where left and right sides meet dorsally.
Orkney 1975.