The means of movement of the common Scallop, or Cockle, and other bivalves, by means of a single fleshy “foot,” have been described in speaking of Molluscs in general; but the spinous Cockles, _Cordium aculeatum_ and _C. tubercutum_, have been termed the aristocracy of the Scallop tribe. The valves of the largest open three-quarters of an inch, and the visible portion of the spongy-looking fleshy mantle is of a pellucid orange colour; at the end is protruded a double tube, thick and short, enveloped in a fringe of cirrhi or tentacles. The foot, which has been compared to a tongue, is smooth, glossy, and semi-transparent, like scarlet cornelian, and enables the creature to move about with great activity in an Aquarium; some that were sent, by the Rev. C. Kingsley, to Mr. Gosse, having startled that gentleman by the noise they were creating among the pebbles and other objects of his tank, by their rapid movements. Many other kinds of shells might be mentioned if space permitted, but I must content myself with mentioning, _en passant_, the polished _Donax_, which, when the animal displays itself, exhibiting its bright yellow colouring, with its curious stripes and gay pink fringes, would form a real ornament to the drawing-room sea; and just hinting at the introduction of a specimen of the _Tritonia Hombergi_, remarkable for a power of producing an audible sound like the click of a steel wire. The pretty little bivalve, the _Lima hians_, also forms a very attractive addition to the Aquarium, especially in motion, when its long orange fringes form a train or tail like that of a fiery comet, as Dr. Landsborough has observed, as it glides along, propelled by the discharge of a jet of water, the mechanism for the propulsion of which forms its swimming apparatus. [Illustration] ------------------------------------------------------------------------ CHAPTER VII. THE ASCIDIANS, BARNACLES, SEA-CUCUMBERS, NAKED MOLLUSCS, SEA-WORMS, ETC. A group of _Ascidians_ forms a very curious object for the Aquarium, their forms being singular, and sometimes delicate as a transparent egg-shell. The group delineated in Plate VII. will convey some idea of the general appearance of these creatures, whose habitations might be taken for a store of fairy pitchers, placed snugly in their submarine china-closet for extra safety, and partially covered with sea-weed as a further means of concealment. There are above fifty native species, varying greatly in appearance. They may be found at the extreme verge of low water, many having the aspect of pellucid bags, formed of a substance between jelly and leather; while others present a far more robust and rugged appearance, both in form and texture. Some are very dingy in colour, but a few species—more rarely found—are very attractive, and sometimes brilliant, in their hues. [Illustration: PLATE X.