(Synonyms: Neritina sand-wichensis Deshayes, 1838; N. convexa "Nuttall," Jay, 1839 (nomen nudum); N. nuttalli Recluz, 1841; ?N. lugubris Philippi, 1843; N. cariosa Gray, Edmondson, 1933.) Length, 20 mm; diameter, 27 mm. Shell: flattened to globose; apex posterior; black but usually eroded. Spire: short, of one and one-half whorls. Sculpture: marked only by fine lines of growth. Aperture: lunate; outer lip thin, sharp, smooth, hinge tooth moderately developed; inner lip with a number of fine, irregular teeth; septum smooth, plane. Operculum: calcareous, opaque, blue-gray with bordering red periostracum; rib and peg sharp. Color: black with gray or yellow spots, palatal lip and parietal areas white.
These animals are abundant in localized brackish water pools on Hawaii and in the more saline parts of estuaries on others of the windward islands. They are
apparently broadly euryhaline, found at salinities of from 1 to 30 °/oo (Maciolek, In press).
T. cariosus is endemic to the Hawaiian Islands.