purple dye murex (Bolinus brandaris) (Gastropod) on a beach in Israel, a sea snail. Murex was at one time greatly valued as the source for purple dye. It discharges a purple ink from the hypobranchial gland in the mantle cavity as a smoke screen, from behind which it can flee. The Phoenicians, centred on Tyre, gathered the snails, crushed & boiled them with salt for several days to extract the ink. The liquid was allowed to cool & over a period of time the colour changed for yellow to green to blue & then a rich purple. The extraction of the ink & the manufacture of purple cloth made Tyre a household word in the past.