Shell moderately large, up to 62 mm. (2,45 inches) in length, very solid, ovate, conical, with the apex subcentral, coarsely sculptured with numerous strong radial ribs, that are rendered scabrous by concentric growth lines, and also strongly corrugate the margin. Colour, externally dull ashen, more or less stained with pale brown; internally, bluish white, corrugated margin bordered in dark-brown, almost black, and the spatula clouded with whitish callus.
Radula-formula: 3 + 1 + (2+1+2) + 1+3. Radula very similar to that of P. caerulea, except that the small slender median central is a definite tooth bearing a small cusp.

This species is unmistakable: it is roundish in outline, it is not much elevated and its aspect is quite solid, massive, it reaches remarkable sizes. Sculpture made by radial ribs large, nodulous (about 40), alternate with other ones in smaller sizes making a denticulation evident on margin. Peristome uneven and sharp. Growth striae quite broad. External surface yellowish in colour tending either to ferruginous or greyish, with spots black in colour. Internally it is white porcelain-like in colour, clear blue in colour, scar of foot quite visible, placed centrally, blackish in colour. Its large radial ribs overflowing from margin make immature specimens too easily definable. As far as this species is concerned, in literature there can be found a lot of synonyms and also of varieties proving its intraspecific variability At present it is to be considered as a protected species. Average measures of adult specimens are around 70-80 mm in length.

Mediterranean, from the Aegean to Spain and North Africa.

Habitat: it lives on rocks in zones particularly exposed at wave motion, in the mesolittoral area.
Distribution: mainly it can be found in the Western Mediterranean. More frequent along coasts of Corsica (France) and of the Tuscan Archipelago islands (Italy).