Habitat: it lives on detrital-muddy bottoms, either sandy or coralligenous ones, in the infralittoral and circalittoral zones. It is found in remarkable depths too.
Distribution: it can be collected all over the Mediterranean. Never common.
Notes: shell solid, equivalve, almost equilateral, valves convex, roundish in form, anterior margin a little bit truncated. Surface adorned by about 26 radial ribs, quite wider than interspaces, covered by lamellae bent, close and strong, more spiny in lateral areas and wider in ventral zone, just giving a rough aspect to surface. Interspaces are narrow and present some dimples not much deep. Generally dirty white in colour, sometimes with maculae either yellowish or light brown. Periostracum light brown in colour. External ventral margin crenulated. It is recognizable from P. papillosum due to its smaller sizes and to its sculpture made by a larger number of papillae which are also smaller. In our opinion some synonymia (P roseum, P. nodosum and other ones) quoted in literature need further confirmation. Average measures of adult specimens are around 7-9 mm in diametre.