Shell a moderately high and sharply pointed cone with a stepped profile. Last whorl markedly keeled at periphery and flat-sided adapical of that; ornament of shallow spiral grooves and ridges. Columella bulging into aperture; inner lip everted to block wholly or partly the umbilicus, which, if open, is comma-shaped. The shell has 6-7 whorls. There are 14-18 spiral ridges on the base of the shell, 16-18 on the adapical part of the last whorl, 14-16 on the penult, the number reducing up the spire. Young animals show an open umbilicus but this is gradually closed by growth of the inner lip. Brownish with blue-green iridescence and scattered brown spots, most marked below the sutures; base paler. Up to 9mm high, 10mm broad; last whorl occupies about 75% of shell height, aperture about 50%.
The body of the animal agrees in most particulars with that of other Gibbula species. The snout is less papillated but has prominent ventrolateral ridges connected to the corresponding eye stalk which is also linked over the tentacle base to a cephalic lappet. The right eye stalk connects with a neck lobe with simple edge and then with the epipodial fold; the left eye stalk and neck lobe are separate, this lobe with a fringed margin. There are three pairs of epipodial tentacles each with a sense organ behind its base. The body is cream with brown and white lines and blotches.

G. tumida is a northern species found between Iceland and northern Norway and Spain. It has been recorded from off most British and Irish coasts; it is not intertidal but may be dredged to 1200 m both amongst weeds and on stones. Its way of life is like that of other Gibbula species. Breeding occurs (Helgoland: Gersch, 1936; Ankel, 1936) in spring, when eggs are laid, each in a jelly coat and aggregated into spawn masses.