Shell an elongate cone of eight or nine tumid whorls; sutures deep, accentuated by a slightly swollen, often beaded subsutural band. Sculpture of strong, flexuous transverse costae (slightly crescentic on upper whorls), spiral striae and growth lines. Spiral striae numerous with major spirals separating small groups of minors: interaction with growth lines gives them a finely beaded appearance and fine reticulate pattern to shell. Protoconch of three or four whorls, initially smooth, becoming tuberculate before merging with teleoconch. Aperture elongate-oval, with a thickened peristome and a short, wide siphonal canal. Outer lip markedly prosocline to base of subsutural band where it adopts an opisthocline plane, forming the anal sinus. Inner lip thickened, delineated by a shallow groove where it reflects over the columella (B. nebula-drawing).
Up to 14 x 5 mm.
Light horn coloured or reddish brown.
Cephalic tentacles with eyes about two-thirds of length from base, tentacle diameter halved distally. Foot shield-shaped, with double-edged anterior; no operculum.
On sand and muddy gravel bottoms from LWST (rarely) to 50 m.
Distributed from Mediterranean to Norway; locally common; absent from eastern Channel and southern North Sea (Distr. B. nebula).