Let us now pass on to the murex2593 and various kinds of shell-fish, which have a stronger shell, and in which Nature, in her sportive mood, has displayed a great variety—so many are the various hues of their tints, so numerous are their shapes, flat,2594 concave,2595 long,2596 crescent-shaped,2597 rounded into a globe, cut2598 through into a semi-globe, arched in the back, smooth, rough, indented, streaked, the upper part spirally wreathed, the edge projecting in a sharp point, the edge wreathed outwards,2599 or else folding inwards.2600 And then, too, there are the various distinctions2601 of rayed shells, long-haired2602 shells, wavy-haired shells, channelled shells, pectinated shells, imbricated shells, reticulated shells, shells with lines oblique or rectilinear, thick-set shells, expanded shells, tortuous shells, shells the valves of which are united by one small knot, shells which are held together all along one side, shells which are open as if in the very act of applauding,2603 and shells which wind,2604 resembling a conch. The fish of this class, known as the shells of Venus,2605 are able to navigate the surface of the deep, and, presenting to the wind their concave side, catch the breeze, and sail along on the surface of the sea. Scallops are also able to leap2606 and fly above the surface of the water, and they sometimes employ their shell by way of a bark.