Ampullosansonia and Tinianella n. gen. are introduced for minute gastropod species from shallow-water, submarine caves of tropical Pacific islands. The species of these genera possess a characteristic protoconch that consists of a smooth protoconch I and spirally granulated protoconch II with a sinusigera aperture, typical of Pickworthiidae (Caenogastropoda). Three new species of the genus Ampullosansonia and one new species of Tinianella are described : Ampullosansonia hyalina, Ampullosansonia fragilis, Ampullosansonia crassicostata and Tinianella tabulata