Shell not glossy, slightly translucent when fresh. The spire is a little cyrtoconoid in profile, the apical angle of young specimens 42-56°, of old ones 16-30°. It is rather tall, the 6-7 whorls each with a marked sutural ramp (which Rives a turreted profile), below which they are moderately tumid sometimes almost Hat al the periphery. The sutures lie below the periphery of the upper whorl, are well marked, slightly incised, and wavy. The base of the shell is a little extended. The ornament consists of costae, spiral ridges and growth lines. The costae are well developed, rather far apart, and high below the sutural ramp. In some shells they appear broadly undulate, in others rather narrow. They start at the suture, run prosoclinally across the ramp (here usually low) and then become orthocline. They cross the whorls of the spire but disappear on the basal half of the last whorl though some traces, along with prominent growth lines, persist and curve to meet the columellar lirae at right angles, overriding and often obliterating the spiral ridges. On older whorls worn costae may present a double summit. Their number varies from 12 to 16 on all except the most adapical whorls. Spiral ridges are slighter than costae except at the edge of the sutural ramp where a larger one interacts with them to produce a marked shoulder; on the ramp itself they are numerous and fine, below it they are broader, higher, more spaced; they are always broader than the intervening spaces and large and small may alternate or their pattern be irregular. There are 30 or so on the last whorl. 9-11 on the penult, decreasing up the spire. On the 3rd (sometimes also the 4th) whorl a reduced number of well-spaced spiral ridges and costae gives a cancellated surface. Fine growth lines cross the spirals and make them slightly ridged. The protoconch measures 750-1150 mu in height and 100-1600 mu in breadth. The first whorl is smooth or has fine spiral lines; on the second 3 spiral keels appear with many fine costellae crossing the spaces between them. The junction of the larval and adult shell is sometimes clear, sometimes not.
Aperture. An elongated oval, angulated above and passing smoothly into the siphonal canal below. The outer lip is thin, has no varix, and arises from the last whorl about the level where the costae fade, perpendicular to the surface. It shows a sharp change of direction at the end of the sutural ramp, and at this point there is a shallow anal sinus. The canal is short and widely open. The columella is very broad, nearly straight, and rather long. The lip here and over the last whorl is expanded outwards so that there is no umbilical groove; it is marked by fine longitudinal growth lines and is pustular. Colour. Biscuit.
Size. Up to 20 x 9 mm, but commonly 12x5 mm. Last whorl = 66% (range 53-73) of total shell height; aperture = 50°/o (range 46-53) of total height.
Animal. There is no snout, the head ending in a transverse fold with the mouth (= opening of a proboscis sac) on the underside. The tentacles, which arise from it bear each a small eye about a third of their length from the tip, the part proximal to the eye twice as broad as that distal to it. The mantle edge bears a siphon on the left, which projects a long way from the siphonal canal as the animal creeps, but is otherwise plain. Males have a penis behind the right tentacle. The foot is shield-shaped, broad anteriorly, slightly indented in the mid-line and angulated laterally. It bears a small, oval operculum posteriorly and dorsally; this has a groove parallel to its columellar margin. Colour. White to grey or brown, with opaque white speckling.

From the British Isles, where it is locally not uncommon, north to the Arctic, extending into the Kattegat and Limfjord. The species is probably circumpolar and reaches south to Massachusetts in the western Atlantic and to Washington in the eastern Pacific.