Shell heights:
1.95 mm, Weymouth 7th April 2012;
1.6 mm, Anglesey, May 2016;
1.5 mm, leg. J.Light, N. Yorkshire, September 2014.
Breadth as % of height (left to right): 54%, 59%, 60%.
Height of body whorl as % of shell height: 64%,75%,73%.
Height of aperture as % of shell height: 36%, 47%, 47%

Fretter & Graham (1978) state 1.5 mm as maximum shell height, but two of these exceed that limit. In winter, numbers decline and mainly juveniles are found, but the very large specimen, 1.95 mm high found in early spring, suggests that a few adults may survive the winter.
Extent and shade of brown pigment on body, visible through transparent shell, vary:
Left: pigment marks coalesced and brown replaced by black.
Centre: typical brown streaks of opercular lobes visible through operculum.
Right: no brown opercular lobes visible through operculum.