Diagnostic characters
Shell small, columnar, with blunt tip; whorls fiat-sided each with subsutural spiral ridge and axial grooves. Confined to leaf litter in woodland on calcareous soils.
Other characters
A glossy, semitransparent shell with narrow, slightly cyrtoconoid spire. There are 5-6 whorls, the last of which occupies about 40% of the total height. The aperture is square to lozenge-shaped, angulated at its apex, with a promin¬ent peristome. The columellar lip all but obliterates an umbilical groove and an umbilicus is absent. The parietal lip is rather prominent and nearly straight. The operculum is thin, with few turns. Yellowish brown, sometimes redder. Up to 2 mm high, 1 mm broad; aperture occupies 20-25% of shell height.
The head extends to a narrow snout with terminal mouth. The tentacles are set far apart, each with an eye behind its base, and a tentaculiform penis arises behind the right eye in males; its edges curl to form a groove connected across the floor of the mantle cavity to the male pore. There is no ctenidium, and the mantle cavity is commonly filled with water containing a bubble of air, the water circulated by cilia on the walls of the cavity (Creek, 1953). The foot is narrow, broader anteriorly, pointed posteriorly. The flesh is nearly transparent with many fine brown spots on the skin, but black at the base of the tentacles and on the mantle skirt.
A. fusca is found under stones and pieces of wood amongst leaf litter in woods, especially beech woods on calcareous soils. It prefers damp, shady places and avoids light. It is generally distributed in the British Isles where these conditions can be met. Abroad, the species ranges eastwards as far as Greece, except Spain and Portugal, and is absent from most parts of Europe north of the Alps.