Closely related to the Tellinidae is the Psammobiidae, a characteristic form of which (Psammobia rubroradiata) is thus spoken of by Prof. Josiah Keep, in his interesting little book, “West Coast Shells:” “But I wanted to see more of him, so I took a large jar, filled it half full of beach sand, added as much sea-water as it would hold, and plunged my prize into the same. He rested quietly for a few minutes, and then began to open his shell and cautiously put out his two siphons. Soon afterward, from between the edges of his shells, came his big, white, spade-shaped foot. He drove it down into the sand, curved it a little to one side, gave a vigorous pull, and lo! his shell followed, though just why I could not clearly understand. Though the jar was large he reached the bottom before his shell was wholly covered with sand, and had to content himself with a half-above-ground tenement.”
“Next morning his siphons were stretched out some six inches in length. * * * I never thought before that there was any particular beauty to the siphons of a clam, but for this red-lined one my opinions quickly changed. Imagine two tubes made of the finest pink and white silk, stretched over delicate hoops arranged at regular intervals; then think of them as endowed with life, and waving with a graceful motion through the water, and you will have a faint idea of their exquisite texture and elegant appearance.”
To those readers who live in the West, away from the ocean, the Unio, or freshwater mussel, is more or less familiar. What child in Chicago has not played on the sands of Lake Michigan and scooped up the little grains with the broken half of a clam shell? Or who, wading in the muddy water of Lake Calumet, has not wondered what the curious little hollow, fringed objects were which protruded from the surface of the mud? These latter were the siphons of the clam and if you were to dig under them a little way you would find the beautiful green-rayed shell of a river mussel. These are no less interesting than the marine shells already described and in beauty of ornamentation they frequently excel many of their salt-water relatives. Such excrescences as knobs, spines and rib-like undulations are common, while the colors of the interior range from pure silvery white through orange, pink and salmon to dark purple, and the rich, pearly iridescence rivals that of any of the marine shells. In many parts of the West mussels are collected by men in search of pearls, which are generally of an inferior quality, and thousands of shells are used annually in the manufacture of pearl buttons.
One of the most familiar objects to the seaside visitor is the huge banks of sea-mussels (Mytilus) which line the shore at low water. The shells are generally dark-colored, our common mussel (Mytilus edulis) being frequently jet black, and are more or less wedge-shaped in form. They attach themselves to mud banks and shore vegetation by a strong byssus made up of stout, more or less silky threads. The mussels are of great value economically, thousands of bushels of the edible mussel (Mytilus edulis) being consumed annually in Europe. They are also used as bait, and millions of the mussels are thus used every year. Although considered a delicacy in parts of Great Britain and Europe, it has not yet been adopted as an article of diet in this country, the clam and quahaug taking its place.
The family Aviculidae, comprising the wing-shells or pearl oysters, is of great interest, both scientifically and economically. At the present time there are a little over one hundred species living, but the family has been known from early geological times and over a thousand species have been found in the rocks. The pearl-oyster (Melleagrina margaritifera) is the most important member of this family, furnishing as it does the beautiful pearls of commerce. These animals are found at Madagascar, Ceylon and other parts of the Indian Ocean, several hundred tons being imported into Europe annually. These pearls are formed by some irritating substance, as a grain of sand or some parasite, getting in between the shell and the animal, or lodging in some soft part, which causes the animal to cover it with pearly matter to prevent irritation. The shells also furnish a considerable part of the “mother-o’-pearl” which is so largely used for ornamental purposes. The Margaritifera radiata, figured on our plate, is a member of this family.
The scallop is an object well known to the tourist visiting New England summer resorts, who has reveled in “fried scallops.” The family to which this belongs (Pectinidae) is composed of rounded shells, many with frills or ribs and nearly all ornamented with beautiful colors. Unlike the animals which we have been considering, these mollusks have no siphons and the shell is open all the way around save at the hinge, and the edge of the mantle is provided with little, round, black eyes. It is an interesting sight to observe a beach at low water, the receding tide having left on the shore or in little pools of water hundreds of these mollusks, attached by a byssus to bits of sea weed. As one is gazing wonderingly over this vast field of yellow sand and green weed, an object will suddenly move through a pool of water with astonishing rapidity, accompanying the movement by a quick snapping sound. This is the scallop, which is imprisoned in the pool and which desires to get out. The movement is effected by rapidly closing and opening the two valves of the shell, thereby causing a clicking sound. The noise of several hundred of these shells opening and closing and the sight of as many scallops with strings of sea weed attached to them, shooting through the water, looking not unlike a comet with a long tail, is quite bewildering. In Europe, the scallop is considered quite a delicacy and several tons are gathered annually. One species (Pecten jacobaeus) has been dignified as a badge of several orders of knighthood and it was also worn by pilgrims to the Holy Land a good many years ago. It was called “St. James’ Shell.”
The most common shell to the layman is the oyster (Ostrea virginica), the cultivation of which occupies the attention of a large number of men and the investment of considerable capital. The oyster is free and active when young, but becomes attached to some submerged object early in life. Oyster culturists take advantage of this habit by erecting poles in the water to which the young oysters attach themselves. The shells of the different species of oyster are not generally of much beauty, but a related family, the Spondylidae, or spiny oysters, are among the most beautiful of bivalves. In this family the shell is ornamented by many long spines and frills, and the colors are different shades of red, yellow and pink. The most beautiful species are found in the Gulf of California.
The space at our command is far too limited to adequately discuss the many curious and interesting animals which make up the class Pelecypoda. Much might be said of the Solen or razor-shell, with its curious foot which is so great a help in digging burrows; of the Pholads, which perforate and make burrows in clay, wood and even in the hardest rock; and of the strange Teredo or “shipworm,” with a long, worm-like body which bores into ships, wharves and any wooden object within reach. But enough has been written and pictured to show the reader that the unpretentious clam, mussel or oyster and their relatives have many interesting habits, are encased in beautiful shells, and that some species are of great economic importance to man.
Frank Collins Baker.