Beautiful shells

by H. G. Adams

THE MUSSEL AND THE COCKLE.

It is in the Dimyaria division of the Conchifera that we must look for these familiar bivalves, the Mussel, or, as it is sometimes spelled, Muscle, and the Cockle; the former called in scientific language Mytilus, which in Latin means simply a shell-fish, and the latter Cardium, which may have reference to the hinge of this bivalve, or the heart-shape assumed by several of the species; cardo, in Latin, signifying the hinge of a gate, and cardesco, a stone in the shape of a heart.

It is to the Mytilidæ family that we shall first direct our attention, and here we find the Common or Edible Mussel, (M. edule,) and many other species, in all of which the shell is more or less elongated, or lengthened out, and pointed at one end. The members of this family are abundant on most rocky coasts, where facilities are afforded for the mollusks to moor themselves to rocks, stones, and other substances covered at high-water, but left dry by the retreating tide. They are not, however, confined to shores of this description, but are sometimes found in vast numbers on low sandy or pebbly flats, which run far out into the sea; these are called beds of Mussels, and are, like the Oyster grounds, specially cared for and protected. As a ship by its cable, so commonly the Mussel, by its bissus or beard, is made fast to its anchorage-ground, be it pebbly or sandy beach, or jutting rock. Sometimes, however, the mollusk travels, and this is how it manages to do so; it has a stout fleshy foot, in shape something like that of a chubby child, and this it can advance about two inches beyond the edge of the shell, then fixing the point of it to a piece of rock or any other body, and contracting it, the shell is drawn onward, and sure, though slow, progress is made in any desired direction. The Pinna, as the marine Mussel is called, has a foot which is cylindrical in shape, and has at the bottom a round tendon, almost as long as itself, the use of which appears to be to gather in and retain the numerous threads with which, when inhabiting the shores of tempestuous seas, it lashes itself fast to the fixed objects around; these threads are fastened at various points, and then drawn tight by the animal, whose instinct teaches it that its brittle shell would soon be broken in pieces, if suffered to roll hither and thither at the mercy of the waves.

The Mussel has a very curious method of preparing its cable for this service; it is not woven, nor spun, nor drawn out of the body, like the web of the spider, but produced in a liquid form, and cast in a mould which is formed by a groove in the foot, extending from the root of the tendon to the upper extremity; the sides of this groove are formed so as to fold over it and form a canal, into which the glutinous or sticky secretion is poured; there it remains until it has dried into a solid thread, when the end of it is carried out by the foot, and applied to the object to which it is to be attached; the canal is then opened through its whole length to free the thread, and closing again is ready for another casting; as if conscious how much depends upon the security of his lines, the animal tries every one after he has fixed it by swinging itself round so as to put the threads fully on the stretch; when once they are all firmly fixed, it seems to have no power of disengaging itself from them; the liquid matter out of which they are formed, is so very glutinous, or glue-like, as to attach itself firmly to the smoothest bodies. The process of producing it is a slow one, as it does not appear that the Pinna can form more than four or five in the course of twenty-four hours. When the animal is disturbed in its operations, it sometimes forms these threads too hastily; they are then more slender than those produced at leisure, and, of a consequence, weaker. On some parts of the Mediterranean coast, as in Sicily, gloves and other articles have been manufactured from the threads of this mollusk; they resemble very fine silk in appearance.

The foot of the Cockle, of which we here give a figure, is commonly employed in scooping out the mud or sand, beneath which it conceals itself; this useful limb assumes the form of a shovel, hook, or any other instrument necessary for the purpose; it appears to be a mass of muscular fibres, and to possess great power. As a boatman in shallow water sends his vessel along by pushing against the bottom with his boat-hook, precisely so does Mr. Cardium travel; he doubles up his foot into a club, and by an energetic use of it as a propeller, makes considerable headway along the surface of the soft sand beneath the waters. In this way, too, some members of the genus solen force their way through the sand; while those called Tellina spring to a considerable distance, by first folding the foot into a small compass, and then suddenly expanding it, closing the shell at the same time with a loud snap; so that you see these sober-looking mollusks are sometimes frolicksome fellows; this is an enforcement of the lesson, judge not by appearances.

Some of the species, both of the Mussel and Cockle families, have very beautiful shells. We give a representation of one of each, on [Plate VIII]. Fig. 2 is the Magellanic Mytilus, (M. Magellanicus,) found chiefly in the Straits of Magellan; it is generally four or five inches long, the shells when polished are very brilliant, the deep purple colour changing into rich violet, as they are held in different lights. In most cabinets the large fan-like delicate shells of the genus Pinna may be observed; the largest species is that called Pinna flabellum, taken in the Mediterranean; it sometimes exceeds two feet in length. The first of these names is a Latin word signifying, besides a shell-fish, the fin of a fish, or the wing feathers of a bird—hence the term pinion; it refers to the fin-like or wing-like shape of this shell. Flabellum means a fan, referring probably to the bissus of the mollusk, which is fine and glossy, like silk, and very abundant.

Many pretty specimens for figuring might be selected from the Naidæ, a family of Fresh-water Mussels, so called from the Naiades, fabulous divinities of the streams and rivers. The shells of many of these, which are of considerable thickness, are lined with the most brilliant nacre, and in these, as might be expected, pearls are sometimes found. One species, abundant in some English rivers, called the Mya Margaritifera, or, as some say, Uno elongates, has long been celebrated for this valuable production. It was most likely with pearls from this mollusk that Julius Cæsar adorned a breast-plate, which he dedicated to Venus, and hung up in her temple. The rivers Esk and Conway were formerly celebrated as British pearl-fishing grounds; a Conway pearl was presented by her chamberlain, Sir Richard Wynn, of Gwyder, to Catharine, Queen of Charles the Second; and in the royal crown of Britain this jewel is said still to occupy a place. Sir John Hawkins, the circumnavigator of the globe, held a patent for the pearl-fishery of the River Irt, in Cumberland. The rivers of Tyrone and Donegal, in Ireland, have, or had, their pearl-bearing Mussels; we read of one which weighed thirty-six carats, (a carat is nearly four grains,) but not being of perfect shape and colour, it was only valued at forty pounds. We also read of another purchased by Lady Glenlealy, for £10, and found to be so perfect and admirable, that £80 was afterwards offered for it, and refused.

These Naidæ have not a bissus like the Marine Mussels, they are therefore never attached to one object; they use their foot as a propeller in traversing the muddy floor of the pond or river, and they have a very funny way of getting along indeed; first, they open the valves of the shell, put out the foot, and after some little hard work, manage to set themselves up on edge; they then proceed by a series of jerks, leaving a deepish furrow in the mud behind them.

We will now go to Fig. 3, the Spined Cytherea, the Cytherea or Venus Dione of naturalists; the meaning of the term is the mother of Venus, who was, as you will remember, the goddess of beauty, given to this shell perhaps because it is entitled to occupy a place at the head of the Cytherea, a genus of the Cardiidæ, or Cockle family, of which genus there are about seventy-eight living species; this, as it is the most rare, is also, perhaps, the most beautiful; it is found in the seas of America, and is remarkable for the row of spines on the hinder border of each valve; these vary much in size and number, being in some individuals long and far apart, in others, short, thick, and closely set. The colour of the shell also varies considerably, being sometimes of a delicate rose colour; at others, more of a claret; at others again, bordering on purple. It was for one of the first discovered specimens of this shell, that £1000 is said to have been given. Truly a Venus of value this; it ought to be called the Queen of Cockles!

Our next example, (see Fig. 4,) is the Spotted Tridacna, (T. maculatus,) the latter term signifying spotted. In the Chamidæ or Clam family, is placed the Tridacna genus, the discovered species of which are not numerous; they are chiefly found in the Indian seas. The one above mentioned claims pre-eminence for beauty. We cannot quite see the applicability of the generic name; Tridacnus, in Latin, signifies to be eaten at three bites, but he must be a man of large capacity indeed who could so devour the head of this family, the Giant Tradacna, (T. gigas,) a single specimen of which has been known to weigh as much as five hundred and seventy pounds; from three to four hundred is by no means an uncommon size. The shell of this giant mollusk is of a very picturesque shape, something like its spotted congener, as we call anything of the same kind or genus, only it is somewhat plainer, and more deeply ribbed and indented. The inside is of a glossy whiteness, and it is frequently used as a basin for garden fountains, or the reception of rills or little jets of water, which sparkle in its stainless hollow. In the church of St. Salpice, at Paris, is a shell of this immense Clam, the valves of which are used as receptacles for holy water; it was presented to Francis the First, by the republic of Venice. Fancy the clapping to of such a pair of valves, when the animal closes its shell in alarm, and the strength of the cable required to moor it to the rocks or coral reef. The spotted species here figured has a solid and heavy shell, very elegantly shaped, and beautifully marked, as will be seen; the greatly reduced size of the figure prevents anything like justice being done to the original.

The above is a figure of the Heart Isocardea, (I. cor,) which is also a member of the Clam family, and one of the most elegantly-shaped shells in the whole range of Conchology. It is a native of the Mediterranean and other seas of Europe, and has been taken in deep water on the West coast of Ireland. We complete this group with a representation of the curious Arcadæ family, or Ark shells, as they are commonly called, because one of the species was thought to resemble the ark built by Noah. Mr. Swainson tells us that the animals of these shells affix themselves to other bodies by a particular muscle, which is protruded through the gaping part of the valves; they also adhere, when young, by means of the bissiform epidermis, or bissus-like outer skin: this species is a native of the Atlantic Ocean and the seas of Europe. The Antique Ark, (A. antiqua,) is very like the Common Cockle, being of a white colour, and heart-shaped. We give below a representation of this shell, and also of the shell of the pretty little Pearly Trigonia, (T. margaritacea,) included in the Arcadæ family; this is a rare species, found only in the seas of New Holland.