Diagnosis: Shell turbinate to high turbinate; sculpture variable, from smooth with 14-21 fine incised lines to 2-5 carinate ribs with strong granules; colour variable, unpatterned grey-white, or dark with white granules, or white with axial black lines or zigzag flames. Penial glandular disc minute; filament vermiform, pointed.
Shell : Mature shell height 3.2-13.3 mm. Shape turbinate to high turbinate (H/B= 1.19-1.57, SH = 1.41—2.16); spire whorls rounded or slightly turreted, suture distinct; spire profile straight; periphery of last whorl rounded, sometimes slightly shouldered and angled at periphery. Columella concave, wide, hollowed at base; eroded parietal area small or absent. Sculpture of last whorl highly variable: smooth shells with 14-21 weak, irregularly spaced, incised lines; usually one rib at periphery and at shoulder, or up to 5 ribs at and above periphery, and 3-4 on base, are enlarged, separated by 1-2 small riblets ; enlarged ribs at and above periphery usually granulose or minutely lamellose ; strongly sculptured shells with 4 carinate ribs bearing small elongate nodules; granules or nodules not clearly axially aligned; spiral microstriae only in grooves. Protoconch 0.26 mm diameter. Colour highly variable: smooth shells grey-white; sometimes with irregular dark marks or occasional dark growth lines; grey-brown to black ground with white nodules; white with black oblique lines or zigzag axial flames ; first 1-3 teleoconch whorls brown to black, and in sculptured shells with white granules or white spiral ribs; aperture dark brown with pale band at base; columella purple-brown.

Uppermost eulittoral and littoral fringe, below the level of E. marquesensis where the species are sympatric in the Marquesas Islands, sometimes at edges of small pools with algae. Most records are from basalt, but the species is also found on coral limestone and sandstone; usually on wave-exposed coasts not sheltered by reefs, always in oceanic situations with clear water. Occurrence in the upper eulittoral has been recorded in the Tokara Islands (Kurozumi 1994). In the Ogasawara Islands it is common at and just above the mean high water mark of spring tides, at the lower limit of the range of the more abundant E. cecillei .

This is a highly variable Echinolittorina species, with shells ranging from almost smooth to strongly carinate and granulose, and from white to patterned. There is a pronounced geographical pattern in this shell variation and three regional forms can be distinguished. Specimens from the Marquesas Islands are grey-white and without conspicuous dark pattern; they are frequently smooth, but the two ribs at periphery and shoulder (rarely more) may be enlarged and granules are weak or absent. The form in Tahiti is distinctive, with dark coloration (brown to black ground, with white granules) and often only the peripheral and shoulder ribs are enlarged . Elsewhere (Tuamotu Is, Samoa, Kermadec Is, Western Pacific) the shells are strongly sculptured with 4-5 strong ribs at and above the periphery, which bear granules or small nodules, and the coloration is often a striking pattern of black lines on a white ground. Extremes of the range of each of these forms overlap.
Molecular data show that this species forms a monophyletic group together with E. hawaiiensis and the pair E. millegrana and E. reticulata, but the relationships are not further resolved (Williams & Reid 2004). Both smooth and sculptured forms of E. cinerea could be confused with E. hawaiiensis ; the latter bears more numerous incised lines on the last whorl of smooth shells (26-47, cf. 14-21 in E. cinerea), while in carinate forms the ribs bear rounded granules rather than elongate nodules; the colour pattern is of large, irregular patches in E. hawaiiensis', the two species are entirely allopatric. One similar species with which E. cinerea is occasionally sympatric is E. reticulata, which reaches Taiwan, the Ryukyu, Ogasawara and Mariana Islands at the eastern extremity of its range. That species is recognized by its white shell with axially aligned granules, between which there may be brown axial lines; in similar shells of E. cinerea the granules are not conspicuously aligned and the pattern is of oblique and zigzag lines. The form of E. cinerea from Tahiti bears a close resemblance to some shells in the E. leucosticta group (e.g. E. leucosticta; E. biangulata; E. philippinensis; E. tricincta), and the range of E. cinerea overlaps with that of E. tricincta at the margin of the western Pacific Ocean. Shells of E. tricincta have a narrower aperture, a rounded inner lip with adjacent eroded area, less strongly carinate ribs, and sharper nodules.

South and West Pacific.
This species is common in the Ogasawara Islands (Fukuda 1993). Occurrence in the northern Mariana Islands is well documented, but recent collecting has not revealed it in Guam (Vermeij et al. 1984, as N. quad-hcincta feejeensis; B.D. Smith 2003), so the MNHN record may be unreliable. Records further west are extremely rare; only a single specimen is known from each of Taiwan, Ishigaki, Okinawa and the Philippines (listed above), and two from the Tokara Islands (Kurozumi 1994). There are numerous collections available from the Loyalty Islands, Samoa, Tahiti and the Marquesas Islands and the species is evidently common there. Records from New Guinea, New Caledonia and Fiji are sparse. Occurrence on the Kermadec Islands is apparently sporadic; most of the collections available in museums (AMS, MNHN, USNM, Wellington Museum) were made by Iredale in 1908, who reported a few localized colonies (Iredale 1910). The absence from the central Pacific (Marshall, Gilbert and Line Is) is real (cf. distribution map of Littoraria coccinea in Rosewater 1970, indicating collecting effort in the same habitat in this area). However, the littorinid fauna of the Solomon Islands, Vanuata, Tuvalu and outer islands of Fiji (where this species can be expected to occur) is poorly known.