The specimens in hand are characterized by 1) elongate-elliptical, elevated, subconical shell at-taining 10 mm in length, 2) apical perforation rectangular-ovate, somewhat larger in the middle, nearer to the anterior end, 3) anterior slope short and steep, straight or slightly concave, 4) posterior slope longer, slanting about 40°, gently convex, 5) aperture slightly arched, 6) interior apical callus posteriorly truncated and 7) sculpture of raised radial ribs and intersecting weaker concentric cords and threads forming a square-reticulated pattern; 17-18 ribs are present at the apex, 36-38 with some finer intermediate ones at the margin; the concentric cords form rounded, elevated knobs on crossing the ribs. Diodora sp. 2 described from Hong Kong (cf. CHRISTIAENS, 1980: p. 64, Fig. 4) closely resembles Diodora quadriradiata in all respects but has 33 ribs at the margin. Diodora ticaonica (Reeve, 1850) is also similar but has a differently shaped apical perforation.

DISTRIBUTION AND HABITAT. Diodora quadriradiata ranges in the West Pacific from Australia to Japan. It is reported to dwell on hard substrates intertidally and just below the low tide mark (KIRA, 1965; CERNOHORSKY, 1978). According to TANTA-NASIRIWONG (1978), the species is also present in western Thai waters, occurring on the underside of littoral coral rubble.
FOSSIL RECORDS. Quaternary of Japan; Holocene of Thailand.