Diagnostic characters
Shell like that of a small B. tentaculata but glossier, with more tumid whorls, deeper sutures, an umbilicus, a rounder aperture which is not angulated adapically.
Other characters
The apex is blunter than that of B. tentaculata, and there are only 4-5 whorls. The inner lip is convex against the last whorl. Horn-coloured, but often greyer than that of tentaculata. Up to 5 mm high, 4.5 mm broad; last whorl occupies 80% of shell height, aperture 50%.
The body of the animal is like that of the previous species but paler in colour, grey or white with black spots, the tentacles and the foot nearly devoid of pigment.
B. leachi occurs in the same situations as B. tentaculata, with which it is often found, though usually less abundant. It has a more restricted distribution in the British Isles, tending to be limited to the south and east. The animals breed in early summer, laying capsules which are indistinguishable from those of B. tentaculata though a little smaller. Young snails emerge in about three weeks. They are probably annuals (de Wit, 1965) though Beer, Korolova & Lifshits (1969) have suggested a life span of 3-4 years.