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.