TYPE LOCALITY. Station TH 78, northeast of Mae Khlong river mouth. Recent. DESCRIPTION. Sinuatodostomia somsaki n. sp. is characterized by 1) slender, somewhat turreted shell attaining 2 mm in height, 2) protoconch globose-helicoid, of slightly more than 2 whorls, nearly one-third immersed in the first teleoconch whorl, 3) teleoconch whorls flat to weakly convex, with sharply angular periphery at the abapical one-third, markedly contracted below this, meeting at grooved sutures, 4) body whorl about 55% of total height; base well convex, rather quickly attenuated, with more or less distinct umbilical chink, 5) aperture oval, rather small, 6) outer lip with U-shaped, moderately deep subsutural sinuation; columellar fold weak, 7) outer surface with faint spiral microsculpture and dense growth lines; a spiral thread lies on the peripheral angulation. The Japanese Sinuatodostomia angustitestulata Nomura, 1939, is closely related, but differs in that has a peculiar pagodalike spire and higher body whorl that tapers less quickly at the base.