Alinda biplicata, also known as Balea biplicata, common name the two lipped door snail or Thames door snail, is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Clausiliidae, the door snails, all of which have a clausilium.

This species is known to occur in a number of European countries and islands including: This species is rare in Great Britain.

In England, it is found mainly in the London area, almost exclusively along the River Thames, and is particularly preserved at Isleworth Ait.

[7] Like all species in this family, this snail has a clausilium.

This spoon-shaped "door" is supported by, and slides in, a series of internal shell folds, see the image below.