Fig. 153.—1. Anomia ephippium. 2. Pecten tigris. 3. Pecten, animal in shell
Native oysters—those that are reared on artificial beds—are of course removed as soon as they are ready for the market, but those that live on natural banks are often left undisturbed till their shells are thick with age. The latter, too, are often destroyed in large numbers by the boring sponge ([p. 124]), which so completely undermines the substance of the shell that it finally breaks to pieces.
In the genus Anomia the lower valve is concave, and perforated with a large oval hole very near the hinge, while the upper one is very convex, but the shell is very variable in shape, since the animal sometimes clings permanently to an object, and the shell, during its growth, accommodates itself to the surface of that object. The use of the hole is to allow of the protrusion of a set of muscles which proceed from the upper valve, and give attachment to a plug or button, more or less calcified, by which the animal clings.
One species (A. ephippium), known as the Saddle Oyster, is common on some parts of our coast. It is seldom found on the beach at low water, but the empty shells are often washed up by the waves.
The same family includes the Scallops, which constitute the genus Pecten. In these the shell is nearly round, with ears on each side of the umbones, those on the anterior side being generally much more prominent than the others, and both valves are ornamented by prominent radiating ribs. The shell is often very prettily coloured, and the animal rests on the right valve, which may be distinguished from the left by its greater convexity, and by the presence of a notch under the anterior ear. The hinge is straight, with a very narrow ligament, and the internal cartilage is situated in a central pit.
Plate V.
MOLLUSCS
| 1. Solen ensis | 8. Tellina |
| 2. Trivia Europæa | 9. Capulus hungaricus |
| 3. Trochus umbilicatus | 10. Chrysodomus antiquus |
| 4. Trochus magnus | 11. Buccinum undatum |
| 5. Littorina littorea | 12 & 13 Scalaria communis |
| 6. Littorina rudis | 14. Pecten opercularis |
| 7. Haminea (Bulla) hydatis | 15. Pecten varius |
| 16. Pecten maximus | |