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.”