Illustrated Index of British Shells Containing figures of all the recent species

SHELL-BEARING BRITISH MOLLUSCA.

A common garden Snail, observed crawling and feeding, is easily seen to possess a distinct head, upon which are four feelers or horns, with eyes at the end, and underneath which is a mouth; a broad disc, extending the whole length of the body, is the organ of locomotion; a spiral or coiled shell surmounts the whole.

If, on the other hand, an Oyster be opened, no distinct head, or place for eyes or mouth, can be seen, but only a seeming mass of pulp, with a round gristle in the centre (the muscle of attachment), the former enclosed in a soft skin with a double fringe round the edge (mantle), placed within a shell composed of two pieces.

All Mollusca are more or less completely represented by these two. The Snail and its class are named Gasteropoda (abdomen-creeping), and their shells Univalves; the Oyster and its class, Acephala (headless), and their shells Bivalves. We begin with the latter class at--

PLATE I.

Pholadidæ, or "Borers," 1-13, have the power of piercing and inhabiting holes in submarine wood, rocks, and stones. The hinder part of the body is lengthened out in the form of a double tube, with openings for the ingress and egress of fluids. Teredo, 1-6, has short valves, two pallets fixed at the sides of the siphons, and lines its hole with a shelly tube. Pholas and Pholadidea, 8-13, have long valves and sometimes accessory plates. The shell of Xylophaga, 7, is like that of Teredo, but the animal has neither pallets nor tube.

Gastrochæna, 14, has a gaping shell, and encloses itself in a bottle-shaped covering of cemented stones and sand. Saxicava, 15, 16, Venerupis, 18, and Petricola, 17, burrow in sand, or live in holes of rocks.

Myadæ, or "Gapers," Mya, 19, 20, and Panopæa, 21, 21*, burrow downwards in sand and mud, their siphons protected by a coriaceous covering. Their shells are not closed all round, and those of Mya have a spoon-shaped process in the hinge of one valve.

Corbulidæ, 22-28, have short siphons with fringed edges, and the foot protrudes through a hole in the otherwise closed mantle.

PLATE II.

Poromya, 1, 1*, and the beautiful pearly Pandora, 2, 3, might be included in the family of Corbulidæ. Lyonsia, 4, and Thracia, 5-10, represent the Anatinidæ. 11-18 are Solenidæ, or "Razor-shells." Solens burrow in deep holes in the sand, where they remain in a perpendicular position at a great depth below the surface, where yet their presence may be traced by the opening left. Their large muscular foot enables them to take great leaps when out of the holes.

PLATE III.

Psammobia, 1-4, and Tellina, 5-16, include some of our most beautiful shells. The animals have a large, fleshy, curved foot, and the mantle open and fringed. Their shells are provided with an external ligament, and teeth on the hinge. Donax, or "Wedge," 19, 20, has long, separated, fringed siphons. Besides the small external ligament, properly so called, the Mactridæ have a triangular pit in the hinge of their shell, containing an elastic substance or spring, designed to resist the action of the adductor muscles. Mactra, 21-26, ends the Plate.

PLATE IV.

Lutraria, 1-3, is another genus of Mactridæ. The Veneridæ, 4-16 and 23, or "Venus" tribe, differ from it in not having the spring-holding pit. Artemis, 10, 11, is known by a large angular bend in the pallial impression; and Cytherea, 23, is distinguished from Venus by one tooth on the hinge standing out a little way from the central ones. Astarte, 17-22, belongs to the Cyprinidæ.

PLATE V.

Fig. 1-3 also represent genera of Cyprinidæ. They have no bend in the palleal impression. Cardium, or "Cockle," 4-13, presents a peculiarity in the foot, which is large and bent, and enables the animal to leap in a very lively manner. The family of Lucinidæ occupy the remaining figures. Lucina has a curious tongue-shaped doubling of the pallial impression.

PLATE VI.

The Kelliadæ, 1-15, are marine, while the Cycladidæ, completing the Plate, are fresh-water bivalves, and may be found in many ponds and rivers.

PLATE VII.

Of the Unionidæ, or "Fresh-water Mussels," Unio, 1-3, has teeth on the hinge, and Anodon, 4, has not: it is a thin shell. The foot of these molluscs is very large, and is used in cutting the animal's way through the mud in which it burrows. Of the marine, or true Mussels, Modiola, 6-9, and Crenella, 12-17, have a portion of the shell reaching beyond the point or apex, which in Mytilus is terminal, 18-21. Dreissina, 5, is shaped like Mytilus, but lives in fresh-water docks. The Mytilidæ attach themselves by means of horny threads spun from the foot, and called a "byssus."

PLATE VIII.

Shells of Arcadæ, 1-14, have the hinge characterized by a series of teeth on each side of the apex. Nucula, Arca, and Pectunculus are easily distinguished. Limopsis, 14, has a spring pit between the two rows. Our figure of Pinna, 16, is from a young specimen: it grows to great size, and spins a very silky byssus. The shell of Anomia, 18, is fixed to rocks, etc., by means of a bony button passing through a hole or sinus in the lower valve. Lima, 22-24, has a light, thin shell, and its mantle is adorned with beautiful fringes. It swims rapidly through the water by the opening and shutting of its valves, and also has the habit, in seasons of rest, of protecting itself by a network or vest of marine fragments strung together by its byssal threads.

PLATE IX.

Contains the shells of our Pectens, or Scallops, 1-16. The animals swim like Lima, as above, and also spin a byssus.

The class Brachiopoda, 17-24, so named because what seem to be organs of locomotion consist of a pair of coiled, ciliated arms, ends the list of Headless Molluscs and their bivalve shells.

PLATE X.

Class Pteropoda, 1-4, contains minute Mollusca, with glassy shells variously formed, and wing-like expansions for swimming.

Chiton, 5-17, or "Coat of Mail," which may often be seen incrusting rocks, commences the Gasteropoda; although seemingly fixed, they are capable of locomotion, using the whole of the oval disc, which may be seen on turning them over, for the purpose. The same may be said of the "Limpet" tribe, Patella, 1-22.

PLATE XI.

This Plate commences with other forms of the Limpet tribe, Fissurella, 1, 2, with a hole at the top; Puncturella, 3, with a fissure near the top; and Emarginula, 4-6, with a slit at the margin. Haliotis, 7, or pearly "Ear-shell," leads to the Trochidæ, or "Tops," 8-27.

PLATE XII.

Ianthina, 1-4, is genus of oceanic molluscs, which are provided with a beautiful floating apparatus, on which the female carries her egg-bags.

Neritina, 5, and the Paludinidæ, 8-11, live in fresh-water. The animal of Paludina is sprinkled all over with bright, golden specks. The Littorinæ, or "Winkles," 12-24, are marine, and frequent the shore among seaweeds. Lacuna, 25-32, belongs to the same family.

PLATE XIII., XIV.

Are small genera, various in their characters and habits, but reasonably included in the last family, Littorinidæ.

PLATE XV.

The animals of Turritella, 1-3, and Cæcum, 6, 7, are not unlike, although the shells are so different; eyes at the base of the tentacles, a short foot, and horny operculum. The somewhat similar animal of Aporrhais, 4, 5, is brilliantly coloured with gold and red. Cerithium, 8-10, differs from Cerithiopsis, 11-15, more in regard to the animal than the shell; the latter animal has a retractile proboscis, and its operculum is not spiral.

PLATE XVI.

Chemnitzia, 1-11, and Truncatella, 12, together with Stylifer, Eulima, and Odostomia, form the family of Pyramidellidæ. Notwithstanding the difference in the shells, the animals are very similar, having a retractile proboscis, and eyes immersed at the base of their tentacles.