The Nassas of France are very destructive to the oyster beds of that nation, an adult “borer” being able to perforate the shell of a large oyster in a single night. So numerous are these pests that a single acre has yielded over a thousand individuals. As a result of these depredations the French oystermen carry on a relentless war against the Nassa, destroying thousands of animals annually. With all this persecution the mollusk still exists and even increases in numbers. The dead shells of this genus are a favorite home for the hermit crabs of small size, and it is to be suspected sometimes that other than dead shells are appropriated. We fear that a sort of piracy is resorted to by the hermit crab, resulting in a kind of “walk-the-plank” end for the mollusk, before the new tenant takes possession of the “home.”
Of the many varieties of tropical shells, few exceed the Volutes, or bat shells, in beauty or variety of coloration. They are found in most parts of the world, although strangely enough none are now living in the seas of Europe, but they are most abundant and more highly colored in the tropics and subtropics. The animal is carnivorous, and the long, fang-shaped teeth are certainly suggestive of predaceous habits. The shells are variously colored, some being mottled, some with zigzag or lightning-like markings, while others have spirally arranged dots and lines. One species (Voluta musica, figured on the plate), has received its name from a more or less fanciful resemblance of the surface of the shell to a musical staff, the spiral lines being grouped in sets of four or five and the dots being arranged as notes. In some specimens this resemblance is quite close. The smooth and polished shell of some volutes is due to the fact that the greater portion is covered by a reflected part of the large foot.
On the sandy shores of subtropical beaches certain graceful and polished animals bury themselves from sight in the sand. These are the olive shells (Oliva) whose bright colors and highly polished surfaces rival even the gaudy Volute in beauty. The foot may be described as plough-shaped and is admirably adapted for digging rapidly in the sand, so that the shell may be hidden from sight on the approach of enemies. The long siphon is thrust up through the canal in the anterior part of the shell and its end protrudes above the sand. The high polish of the surface is due to the shell being enveloped in the voluminous foot; hence it has no epidermis. The aperture is so narrow that it is difficult to understand how the animal gets in and out. The olives are very numerous in individuals; when one is found hundreds are sure to reward a patient search.
Probably no more distinct family of mollusks exists than the Conidae, the family of cones, their beautifully decorated shells and the large number of species making them a favorite with collectors. The shell is in the form of an inverted cone, gracefully rounded, the aperture being but a narrow slit extending nearly the whole length of the shell. The colors of the cones are always very brilliant, although when they are alive the shell is not brilliantly polished as the olives, on account of the presence of an epidermis. About three hundred species are known, living principally in tropical seas. They love to conceal themselves in holes in the rocks and among the branches of corals. The animal is predaceous, boring into the shells of other mollusks and extracting the juices from the bodies. The teeth of Conus are hollow and very sharp and have a barb on the end. A poison gland is said to be present in this genus and bites from the animal are very painful, although not dangerous, the large Conus marmoreus being able to inflict a severe wound. The cone is quite pugnacious and will immediately bite the hand when picked up, a veritable reptile of the ocean.
The ne plus ultra of mollusks to the collector is without doubt the genus Cypraea, comprising the cowry shells. So eagerly have they been sought by wealthy collectors that the price of rarities has gone up to an astonishing degree, some specimens being sold at several hundred dollars each. The shell is highly polished, owing to the fact that two lobes of the voluminous mantle are turned back over the shell and meet in the middle of the back. The foot is very large and spreading, the mantle beset with curious little tentacular-like organs and the eyes are placed on small swellings near the base of the long, cylindrical tentacles. The color-patterns of the shell vary to a wonderful degree. The young shell has a thin epidermis, a sharp lip to the aperture and a more or less prominent spire, the rolled over and toothed lip and polished surface not being acquired until fully adult. No more beautiful sight can be imagined than one of these gorgeous animals, as seen through the clear water, crawling over the sandy bottom or on the branch of some coral.
Several of the cowries have a curious economic value. Thus, Cypraea aurantia, the orange cowry, was used as an insignia of royalty by the chiefs of the Friendly Islands, and for a long time the only specimens obtainable were those which had been bored and used. The money cowry (Cypraea moneta) has been used as money by the natives of Western Africa, and many tons of this small shell were annually imported to England to be used in barter by the African traders. The shell is of a yellowish or whitish color, does not exceed an inch in length, and is very common in the Pacific and Indian Oceans. It is still used as a medium of barter in parts of Africa, although other things have pretty generally taken its place.
Cameos were at one time quite in the fashion, both as ornaments for the person in the way of brooches, and as bric-a-brac about the room. These shell-cameos are made from the genus Cassis, the helmet shells. These are well adapted for this purpose, as the shell is made up of several differently colored layers, making a bas relief figure not only possible but very effective. The black helmet (Cassis madagascariensis) is one of the best for this purpose, the figure being carved from the white, outer layer of shell, which stands out very clearly against the black background of the second layer. When a cameo is desired simply as a brooch or for any other form of personal adornment, a piece of the shell is cut out and shaped into the required form and size—oval, square or other shape—and cemented to a block of wood. The figure is then traced on the shell with a pencil and finally carefully worked out with sharp, pointed steel instruments, of delicate size and form. The same process is resorted to in working out a bas relief on the entire shell, only the latter is placed in a vice or other object to hold it firmly. The home of this industry is Genoa and Rome, Italy, although some are produced in France; these latter, however, are of a poorer quality. Several thousand people are employed in this trade. Many beautiful examples of this work were exhibited at the World’s Columbian Exposition, in Chicago, in 1893.
The cameo shells are among the largest of sea snails, several of them measuring eight or ten inches in length and weighing several pounds. They are found only in tropical and subtropical seas, living in comparatively shallow waters on a sandy bottom. They are voracious eaters, living principally on bivalve mollusks.
One of the most abundant of mollusks is the violet sea snail (Ianthina communis), which spends its life floating in the waters of the Atlantic Ocean. The shell is very delicate, resembling in form some of the land snails, and has but two colors, both shades of violet, a deep color on the under side (which, by the way, is always turned upward when the animal is floating in the water), and a lighter shade on the upper side. So fragile is the shell that it seems as if a breath would break it. The most interesting fact in connection with this mollusk is the wonderful float or “raft” which is secreted by the foot, and to the under side of which the eggs are attached. The latter are not all in the same condition. Nearest to the animal they are more or less fresh; those in the middle of the float contain embryos and fully formed young, while those on the outer end are empty, the young having escaped into the water. The genus is gregarious and may be found in almost countless numbers. After a severe storm they are sometimes cast upon the beaches in vast numbers, where they soon die under the fierce rays of the sun.
We have thus far been dealing with snails whose shells were formed in a spiral coil. Quite a number of mollusks are not protected by such a shell, its place being taken by a flat, shield-like disk, or several distinct plates placed side by side. The most familiar of the first is the limpet or Patella, which is a depressed, conical, oval disk, looking not unlike a miniature shield. They live on rocks, to which they cling with great tenacity. The animal seems to have a pretty clear idea of local geography, for it invariably returns to the same place after its excursions for food and the rock in some localities has been hollowed out to a considerable depth by the continuous dwelling thereon of the limpet. The large foot is very strong and it is almost impossible to dislodge the shell from the rock when the animal becomes alarmed and is aware that danger is near. While grazing along the sides of a rock covered with fine sea-weed, it will leave a track like a worm and will clean off quite an area in a very short space of time.