The thin, varnish-like, faintly yellowish periostracum gives the live white shell an ivory white colour, but it may be eroded from dead specimens or, as with these specimens after 44 years in storage, the periostracum may darken.
Maximum height in Britain is 6.5mm. In this sample of 41 from Orkney, 85% were 3mm to 4.5mm high, 5% 5.5mm high and 10% under 3mm height, though smaller specimens were probably commoner but overlooked by the collector.
There are reports of L. bidentata to 8mm high beyond Britain, but it is possible that they are misidentifications of bleached, dead shells of Myosotella myosotis which sometimes, like L. bidentata, has only two protrusions in the aperture.
In crevice between strata of Devonian sandstone (Stromness flagstone), sheltered bay, not salting. Orkney, Scotland. Leg. I.F.S. in May 1975; photographed February 2019.