The Naturalist on the Thames | Page 5

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