These small snails are quite distinctive, because they have
shells that are sinistral, which means that if you hold the shell such that the spire is pointing up, then the aperture is on the left-hand side.
The shells of Aplexa species have a long and large
aperture, a relatively high and pointed
spire, and no
operculum. The shells are thin and corneous and rather transparent.
^Fleming J. (1830). Mollusca. pp. 598-635, in: Brewster D. The Edinburgh Encyclopædia. In eighteen volumes. Volume XIV [= 14] [MED-MUS]. pp. [1], 1-748, Pl. CCCLXXII-CCCC [= 372-400]. Edinburgh. (Blackwood).