Newcomb's snail is unique among the Hawaiian snails in that the shell spire, typically associated with snails, has been substantially reduced. The result is a smooth, black shell formed by a single, oval whorl, 6 mm (0.25 in) long and 3 mm (0.12 in) wide. This lymnaeid snail is threatened and endemic to the island of Kauai. Newcomb’s snail is an obligate freshwater species.