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.