Shell. Solid, opaque; young shells and the less exposed parts of older ones slightly glossy. Generally conical in shape and almost always a little dome-shaped (cyrtoconoid) though not so much as umbilicalis, with flat base and an angulated body whorl (80-85°). Apical angle of shell 70-100°, commonly 85-90° in mature shells but noticeably more (90-125°) in young ones; occasional older shells retain this squatter shape. There are 5-6 whorls, slightly swollen and dipping a little to sutures which are well marked on young shells and older whorls of old ones but may be indistinct elsewhere. Sutural angle approaches 180°.Below each suture the whorls may be a little flattened, giving a slightly turreted profile. The ornamentation is spiral ridges and grooves, and growth lines. The ridges are low and the furrows shallow, both variable in disposition: body whorl (above keel) — 6-15, commonly 8-10; penultimate 7-11, commonly 8-9; antepenultimate 7-10, fairly regularly 8-9. They are rarely of equal size or equidistant, though more nearly so on younger whorls; there is commonly a group of low, narrow ridges at the periphery of the body whorl and each whorl makes contact with the previous at this level, sometimes obscuring all, sometimes exposing a few. There are 10-17, most frequently 13-14, ridges on the base. Most spiral ridges show an alternation of elevations and depressions along their length. Growth lines are prosocline, curving back from the suture on the adapical parts of the whorls, the concavity facing up the whorl towards the apex; on the base the curvature is reversed so that each line is S-shaped. They are commonly visible only in the spiral furrows. Erosion may destroy all ornamentation and expose the underlying nacre. The umbilicus is rather small, its mouth egg-shaped, the narrow end pointing to the origin of the outer lip; in eroded shells the umbilical cavity may tunnel through the whole shell with loss of the apex. Apex depressed, of 1,25 whorls, with a pointed, reversed tip, smooth and about 140 mu across.

G. cineraria is one of the commonest intertidal molluscs on rocky shores with varied surface but without too great exposure, preferring flatter to steeper shores. It is found on and amongst weeds, under stones and ledges, and in pools, from about L. W.N.T. (sometimes higher in pools) to depths of 130 m; they live where the salinity may be as low as 25%c (Nelson-Smith, 1967; Arnold, 1972). The species occupies a belt on the shore at a lower level than that occupied by G. umbilicalis where the two occur together. The animals are to be found on all suitable British and Irish coasts, often in very large numbers, especially in the North Sea and in the north, where the animals are both larger and darker in their coloration. They eat weeds and their epiphytes and are also detritivores. The species ranges from Gibraltar to Iceland.