Of all the gastropods none excel the curious Xenophora in point of oddity. The shell is in general form like that of the top shell, but as it grows it attaches to itself small stones and pieces of shell, so that when the animal is fully grown it looks like a heap of dead shells and pebbles. This habit is in all probability to conceal the animal from its enemies. They are called “carriers” and the individuals with shells attached to their house are called Conchologists, while those with stones attached are called Mineralogists. The fragments of shells are attached with concave sides upward so as not to impede the animal during locomotion. The carriers are not able to glide like other mollusks, their feet being very small. They progress by lifting the front part of the foot to an object and then drawing the hind part toward it. In this way they jump or scramble along in a ludicrous manner.
Related to the “carriers” are the slipper-shells (Crepidula), the horse-hoof shell (Hipponyx) and the bonnet-limpet (Capulus). The slipper shells are found in many parts of the world and are particularly abundant on the Atlantic and Pacific shores of the United States. The shell is flat and somewhat limpet-like, and across one end, near the apex, is a little shelf which gives it the appearance of a Chinese slipper. They adhere to stones, shells, crabs and any submerged object, and modify the form of their shell to fit the inequalities of their resting place. Thus a Crepidula on a Pecten shell will be ribbed while the same species on a stone will be perfectly smooth. Frequently they may be seen piled one upon another in tiers of six or more. The animal generally feeds on seaweed but has been known to eat other mollusks. The bonnet limpets also belong to this family, as do the cup-and-saucer limpets (Calyptraea).
The family Strombidae contains many large and interesting shells. The animal is very powerful and is able to leap a considerable distance. Mr. Arthur Adams, a celebrated conchologist, thus describes its method of leaping: “Planting firmly its powerful, narrow operculum against any resisting surface, it insinuates it under the edge of its shell and by a vigorous effort, throwing itself forwards, carrying its great heavy shell with it, the animal rolls along in a series of jumps in a most singular and grotesque manner.” The eyes of the animal are greatly developed. The shells of Strombus vary greatly in form and color. In some the outer lip is simply turned over while in others it is modified by little spines or projections. The aperture is frequently colored pink, purple or yellowish. The large Strombus gigas is used in carving cameos, its shell being made up of several layers of different colors. It is also ground to powder for the manufacture of porcelain and in the West Indies the animal is used as an article of food.
The Auger or steeple shells, belonging to the family Terebridae, have long been objects of interest not only to the naturalist but to the layman who places them in his house as ornaments. There are about two hundred species which are found in many parts of the world, although chiefly confined to tropical seas. The shells are very long and are composed of many tightly wound whorls, which are smooth in some species and longitudinally ribbed in others. They vary also in color, being yellowish, grayish or brownish, and many species are spotted with red or white.
A group of handsome mollusks live in the tropics whose shells have been named Mitra by the naturalist Lamarck from their fancied resemblance to the Pope’s miter. The shells are fusiform, very thick and heavy and beautifully ornamented with various colors. The surface of the shells of some species is smooth, others granulose and not a few spirally lined and longitudinally ribbed, while the columella is marked by several heavy plaits or folds. There are about two hundred species of this genus, living in all parts of the world but being more numerous in tropical regions. The Philippine Islands seem to be the metropolis of this mollusk, as of others, and their shores fairly teem with the graceful creatures. Some of them live among the coral reefs, concealing themselves in holes or among the sea weeds or under stones. Others live on the sandy or muddy beaches in which they bury themselves when the tide recedes.
The earlier naturalists were fond of applying significant names to the shells which they described and the Mitras have received their share. Thus we have the episcopal miter, having a white shell with brilliant red spots and flame; the papal miter, with a brown-spotted white shell; the pontifical miter, with a red-spotted shell and a coronated spire, and lastly the cardinal’s miter. These four species might be called the ecclesiastical quartette.
The Harp shells, although few in species, are among the most showy of the marine snails. The shells are large and marked by many elevated ribs extending longitudinally, giving the effect of the strings on a harp, hence the name of the genus. The colors are different shades of brown which form neat festoons of dark brown lines between the ribs. The inner lip of the shell is marked by a dark brown spot and another spot is frequently developed near the upper part of the whorl. In one species (Harpa rosea) the shell is marked by several rosy spots and tints, and is very beautiful. The animal of this genus is no less interesting than the shell, being variegated with many beautiful colors. The foot is long, crescent shaped in front and becomes narrowed to a point behind. The animal is said to voluntarily break off a piece of its shell when irritated, as it is not able to retreat within the shell, being destitute of an operculum. It is very active and crawls about with an easy, graceful motion. Harpa lives only in the tropics and is found in the Indian and Pacific Oceans and on the west coast of America.
The Bubble shells include within their number many curious and interesting animals. The typical genus, Bulla, numbers some fifty species of smooth, globular shells, frequently mottled like a bird’s egg. The aperture is as long as the shell and the outer lip is thin and sharp. The animal is large and fleshy and partly envelops the shell. The bubble shells love sandy mud flats in which they bury themselves or find concealment under masses of sea weed. Like many land shells they exude vast quantities of mucus to moisten their skin when the tide is out. These animals are carnivorous, living on bivalves and snails, which are swallowed whole and reduced to fragments by the huge, calcareous gizzard. Not all the mollusks of this order have true shells. The so-called sea hares, have large, flabby bodies in which is lodged a small, oblong, transparent shell. This animal lives among the sea weed, feeding upon the weed as well as upon mollusks and other animals. It discharges a violet liquid when handled which caused the ancients to believe that it was poisonous. The old Greek philosophers wrote a great deal on this subject, believing that to even touch the animal with a stick would cause death. Though repulsive looking creatures they are perfectly harmless and are even eaten raw by the natives of the Friendly and the Society Islands.
Frank Collins Baker.