Surveys over the last 15 years have revealed that the assimineid Paludinella littorina (delle Chiaje, 1828) is much commoner in the British Isles than previously believed. It is currently known living at 40 sites ranging from the Isles of Scilly, eastwards along the Channel coast of England as far as the eastern end of the Isle of Wight. It extends as far north as the Bristol Channel with sites on the north coast of Devon and the coast of Pembrokeshire. The west coast of the Lizard peninsula, Cornwall and the Isles of Scilly support significant numbers of P. littorina populations. The two principal habitats in which we have found P. littorina are caves, and shores with a supra-littoral zone comprising large stones and boulders with stable interstitial gravels beneath. Observations on the species' habitats, ecology and conservation are discussed.