Axial sculpture made up of strong ribs, with interspaces twice as wide as the ribs; spiral sculpture made of slightly narrower cordlets; the whole draws a rectangular cancellation, with rectangular nodules at the intersections; columella slightly sinuous anteriorly, strongly angled posteriorly. Pattern of white blotches, rarer than in purpurea; occasional presence of a white spiral line; an axial white line is also reported sometimes. The shell is more globose than that of purpurea.

« This species has frequently been confused by older authors with R. purpurea, resulting in myriads of historical records of R. purpurea from the Mediterranean, which are very likely to be actually based on specimens of R. atropurpurea. […] R. atropurpurea is easily distinguished by its lower whorls, the less deep suture, the subrectangular aperture, the more regular cancellate sculpture, the less evident cordlets, the shorted siphonal canal and the resulting squatter outline. The coloration is usually monochrome and darker. » – Pusateri & al.: “A revision of the Mediterranean Raphitomidae (Neogastropoda, Conoidea) 4: The species of the group of Raphitoma purpurea (Montagu, 1803) with the description of a new species”, Bollettino Malacologico vol. 53(2), Milano 2017, p.175. The suprasutural white band is commonly found.

Protoconch multispiral of 2,8 whorls, keeled on the last 0,7 whorl. « Shells without the protoconch could sometimes be confused with R. philberti (which has a paucispiral protoconch) but the latter is usually smaller, and has more spaced spirals. » – Ibid. Subadult from Llançà, Alt Empordà, NE. Catalunya, NE. Spain. 5,5mm.