The Ianthinæ, or purple Sea-Snails, carry under their foot a vesicular organ like a congeries of foam-bubbles, that prevents creeping, but serves as a buoy to support them at the surface of the water.
Murex haustellum.
When the sea is quiet, these little creatures,
Like little wanton boys that swim on bladders,
appear in vast shoals on the surface, but as soon as the wind ruffles the ocean, or an enemy approaches, they at once empty their air-cells, contract their float, and sink to the bottom, pouring out at the same time a darkened fluid like that of the Aplysia or the Murex, which no doubt serves them as a defence against their foes, and, according to Lesson, furnished the celebrated purple of the ancients. The Ianthinæ inhabit the Mediterranean and the warmer regions of the Atlantic, but especially towards the close of summer they are frequently drifted by the Gulf Stream to the west coast of Ireland.
Magilus antiquus.
