Shell a moderately tall, rather broad cone. The spire is noticeably cyrtoconoid and has a turreted profile. There are seven postlarval whorls (those of the protoconch often lost) meeting at sutures made sinuous by the uprising ends of the costae. Whorls with subsutural shelf, sutures just below periphery of each whorl. Last whorl occupies about half of shell height (usually slightly less). Ornament of narrow, mainly orthocline costae and spiral ridges in the intercostal spaces. The costae are much narrower than the intervening spaces; there are 16-22 on the last whorl where they fade below the periphery, 17-19 on the penult whorl. The last whorl has 20-25 spiral ridges, the penult 10-12. Aperture square to rhomboidal, occupies about 30 % or less of shell height. No true umbilical groove or umbilicus. Tooth absent though usually there is a slight bulge on columella.
Up to 6 x 2 mm.
Cream with two, occasionally three brown spiral bands on the last whorl; one coloured spiral band lies at the periphery, another is subperipheral and these two are regularly present; a third is subsutural but this may be absent.
The tentacles are triangular, grooved along the lateral margin, rather longer and narrower than in most species. The mentum is long and narrow, dorsally grooved and bifid distally where the proboscis opens. The eyes lie between the tentacle bases. There is a lobed projection on the mantle skirt on the right. The foot is short, truncated anteriorly, with a median embayment and extended lateral points, pointed posteriorly. White with numerous white spots and a general reddish tinge; the foot has white streaks alongside the operculum and there is yellow on the mantle edge.
The animals occur 5-10 m deep, usually with the hydroids Halecium and Antennularia , on which they feed.
Ranges from the Mediterranean to southern Scandinavia; not in the southern North Sea (Distr. T. jeffreysii).