Lapis Judaicus or the Jews' stone: the folklore of fossil echinoid spines

'Jews' Stone' (Lapis Judaicus) is the name given to the spines of certain cidaroid echinoids, especially Balanocidaris. Used extensively as a prophylactic and treatment for various common and painful urinary disorders, particularly bladder stones, kidney stones and dysurea, it has a long folklore pedigree extending from classical times, especially in the Mediterranean area. The medicinal application of the Jews' stone was determined by its shape, using the principle of sympathetic magic. Either sucked or powdered and mixed with a wide range of botanical, mineral and animal ingredients, it was often taken in wine or water. On Malta, echinoid spines were referred to as St Paul's stick.