Typical sizes in Britain (adults usually 8-12mm high). Convolute shell, i.e. all earlier whorls concealed by enveloping final whorl.
1: smallest specimen palest as pigmented layer deposited by external mantle is thinner than on larger older specimens.
2: shell broadest towards apical end (posterior of animal).
3: slight mound indicates position of hidden apex.

Heights (longest shell-dimensions) 8.7 mm, 9.6 mm, 11.2 mm. Ardnamurchan, Scotland. April 1976.