Of the thousands who boat on the Thames during the summer few know or notice the beauty of the river shells. They are among the most delicate objects of natural ornament and design in this country. Exquisite pattern, graceful shapes, and in some cases lovely tints of colour adorn them. Nature has for once relaxed in their favour her rigid rules, by which she turns out things of this kind not only alike in shape, but with identical colour and ornament. Among humming-birds, for instance, each bird is like the other, literally to a feather. The lustre on each ruby throat or amethyst wing shines in the same light with the same prismatic divisions. But even in the London river, if you go and seek among the pebbles above Hammersmith Bridge when the river is low, you may find a score of neretina shells not one of which is coloured like the rest or ornamented with exactly the same pattern, yet each is fit to bejewel the coronet of some Titania of the waters. A number of these tiny shells, gathered from below the bridge, lie before the writer, set on black satin to display the hues. They look at a little distance like a series of mixed Venetian beads, but of more elegant form. From whichever side they are seen, the curves are the perfection of flowing line. The colouring and ornament of each is a marvel and delight. Some are black, with white spots arranged in lines following the curves, and with the top of the blunt spiral white. These "black-and-white marble" patterns are followed by a whole series in which purple takes the place of black, and the spots are modified into scales. Then comes a row of rose-coloured shells, some with white lance-heads, or scales, others with alternate bands of white scales and white dots. Some are polished, others dull, some rosy pink, others almost crimson. Some are marked with cream and purple like the juice of black currants with cream in it. In some the scale pattern changes to a chequer, some are white with purple zig-zags. And lastly come a whole series in pale olive, and olive and cream, in which the general colour is that of a blackcap's egg, and the pattern made by alternate spots of olive and bands of cream. If these little gems of beauty come out of the London river, what may we not expect in the upper waters of the silver Thames?[1] A search in the right places in its course will show. But these neretinae are everywhere up to the source of the river, for they feed on all kinds of decaying substances. If the pearl is the result of a disease or injury, the beauty of the neretina is a product or transformation from foul things to fair ones.

As the Thames is itself the product and union of all its vassal streams, an "incarnation" of all the rest, so in its bed it holds all the shells collected from all its tributaries. Different tribes of shells live in different waters. Some love the "full-fed river winding slow," some the swift and crystal chalk-stream. Some only flourish just over the spots where the springs come bubbling up from the inner cisterns of earth, and breathe, as it were, the freshness of these untainted waters; others love the rich, fat mud, others the sides of wearings and piles, others the river-jungles where the course is choked with weeds. But come what may, or flourish where they please, the empty shells are in time rolled down from trout-stream and chalk-stream, fountain and rill, mill-pool and ditch, cress-bed and water-cut, from the springs of the Cotswolds, the Chilterns, the downs, from the valleys of Berkshire, Buckinghamshire, Surrey, Gloucester, Oxford, and Essex, into the Thames. Once there the river makes shell collections on its own account, sorting them out from everything else except a bed of fine sand and gravel, in which they lie like birds' eggs in bran in a boy's cabinet, ready for who will to pick them up or sift them out of it. These shell collections are made in the time of winter floods, though how they are made or why the shells should all remain together, while sticks, stones, and other rubbish are carried away, it is impossible to say. They are laid on smooth points of land round which the waters flow in shallow ripples. Across the river it is always deep, swift, and dark, though the sandbanks come in places near the surface, and in the shallows grow water-crowfoot, with waving green hair under water, and white stems above it. The clean and shining sand shelves down to the water's edge, and continues below the surface. Here are living shells, or shells with living fish in them. In the bright water lie hundreds of the shells of the fresh-water mussels, the bearers of pearls sometimes, and always lined with that of which pearls are made, the lustrous nacre. The mealy masses of dry sand beyond the river's lip are stuffed with these mussel shells. They lie all ways up, endways, sideways, on their faces, on their backs. The pearl lining shines through the sand, and the mussels gleam like silver spoons under the water. They crack and crunch beneath your feet as you step across to search the mass for the smaller and rarer shells. Many of those in the water contain living mussels, yellow-looking fat molluscs, greatly beloved of otters, who eat them as sauce with the chub or bream they catch, and leave the broken shells of the one by the half-picked bones of the other. There was a popular song which had for chorus the question, "Did you ever see an oyster walk upstairs?" These mussels walk, and are said to be "tolerably active" by a great authority on their habits. They have one foot, on which they travel in search of feeding ground, and leave a visible track across the mud. There are three or four kinds, two of which sometimes hold small pearls, while a third is the pearl-bearer proper.Unio pictorum is the scientific name of one, because the shells were once the cups in which the old Dutch painters kept their colours, and are still used to hold ground gold and silver for illuminating. The pearl-bearing mussel is longer than the other kinds, flatter and darker, and the lining of mother-of-pearl is equal to half the total thickness of the shell.[2]

Though not so striking from their size and pearly lustre, there are many shells on the Thames sandbanks not less interesting and in large numbers. Among these are multitudes of tiny fresh-water cockle shells of all sizes, from that of a grain of mustard seed to the size of a walnut, flat, curled shells like small ammonites, fresh-water snail shells of all sizes, river limpets, neretinae, and other and rounder bivalve shells allied to the cockles. The so-called "snails" are really quite different from each other, some, the paludinas, being large, thick-striped shells, while the limnaeas are thin, more delicately made, some with fine, pointed spiral tops, and others in which the top seems to have been absorbed in the lower stories. There are eight varieties of these limnaeas alone, and six more elegant shells of much the same appearance, but of a different race.

The minute elegance of many of these shells is very striking. Tiny physas and succineas, no larger than shot, live among big paludinas as large as a garden snail, while all sizes of the larger varieties are found, from microscopic atoms to the perfect adult. Being water shells, and not such common objects as land shells, these have no popular names. The river limpets are called ancylus fluviatilis. Some are no larger than a yew berry, and are shaped like a Phrygian cap; but they "stick" with proper limpet-like tenacity. On the stems of water-lilies, on piles, on weeds and roots in any shallow streams, but always on the under side of the leaves, are the limpets of the Thames. The small ammonite-like shells are called planorbis, and like most of the others, belong also to the upper tertiary fossils. They feed on the decaying leaves of the iris and other water plants, and from the number of divisions on the shell are believed to live for sometimes twenty years. Of the many varieties, one, the largest, the horn-coloured planorbis, emits a purple dye. Two centuries ago Lister made several experiments in the hope that he might succeed in fixing this dye, as the Tyrians did that of the murex, but in vain. There are eleven varieties of this creature alone. It is easier to find the shells than to discover the living creature in the river. For many the deep, full river is not a suitable home; they only come there as the water does, from the tributary streams. Far up in some rill in the chalk, from the bed of which the water bubbles up and keeps the stones and gravel bright, whole beds of little pea-cockles may be found, lying in masses side by side, like seeds sown in the water-garden of a nymph.

[1] I have a series of neretina shells from the Philippines, much larger in size and brown in colour, in which many of the same kinds of ornament occur.

[2] A fresh-water mussel shell from North America in my possession is coloured green, and so marked and crimped as to resemble exactly a patch of water-weed, such as grows on stones and piles.