Cirsonella extrema is a species of sea snail, a marine gastropod mollusk in the family Skeneidae. The height of the yellowish white shell attains 2.7 mm, its diameter 2.9 mm. The spire contains 3½ whorls. The round aperture is somewhat oblique. The peristome has a thickened callus, expanded on the left side. Its top is attached to the penultimate...