:< SHELLS " 311 



the shell, the oyster covers it with the same material (called Nacre], and this 

 forms a pearl. 



2. The Saddle Oyster (Anomia ephippium). Very often mistaken for a 

 young oyster of the edible species. This species attaches itself to a rock by a 

 muscular plug, which passes through an oval hole in the under shell near the 

 hinge and sticks like a sucker to the rock. It may often be found attached to 

 other molluscs, and hence derives its name of " SADDLE " OYSTER. 



As it grows older it has the habit of altering its form, to adapt itself to the 

 object on which it rests. 



3. The Cockle (Cardium edule). One of the commonest objects of the sea- 

 shore, with its shells marked with bold ridges. The cockle gains its name 

 of Cardium (Greek kardia, " heart ") from the heart-shaped appearance of 

 the shells when viewed end on. It lies buried underneath the sand, and I 

 have no doubt many of my readers have seen the spouts of water rising from 

 the sand at low tide, the sign of the cockles buried below. It needs skill to dig 

 them up, for the cockle possesses a powerful " foot," and can often burrow 

 faster than a man can dig. 



4. The Spiny Cockle, or RED NOSE (Cardium aculeatum), has a " foot " 

 of a bright red colour. It is much larger than C. edule, has spines or prickles 

 on its shells, and is much sought after for food. 



5. The Mussel (Mytilus edulis). Found often on the submerged piles of 

 piers and breakwaters, where it has fastened itself down firmly, in clusters, by 

 means of a bundle of threads known as byssus. So strong is this thread that 

 mussels are valuable on many parts of the coast in keeping structures from 

 being damaged or disturbed by the force of the water. The story of the 

 bridge across the Torridge River is too well known to be repeated here as an 

 illustration. 



6. The Horse Mussel (Modiola modiolus), 5 or 6 inches long, is found 

 occasionally on the beach. It is a burrowing mollusc, and weaves its byssus 

 into an enormous tangled mass with sand or gravel. It is not used for food. 



7. The Variable Scallop, or PECTEN (Pecten varius). Scallops are familiar 

 to us, if only by means of the fishmonger's shop, where the largest British 

 species, the Common Scallop, QUIN, or PECTEN (Pecten opercularis), is sold for 

 food. This is a deep-sea species, occurring in beds. It is not fixed like the 

 oyster, but can swim in a curious way by opening and shutting its shell quickly, 

 thus expelling the water and shooting itself to some distance. (The young, 

 however, can attach themselves to rocks by means of byssus.) As it moves 

 through the water it waves up and down a fringe of graceful feelers, by which 

 it obtains its food. At their base is a row of black dots, said to be eyes. All 

 scallops have a peculiarity in the pair of ears at the hinge of the shells ; these 

 ears are never of equal size. 



The Variable Pecten is so called because it varies so much in colour 

 crimson, pink, yellow, or white, with dark red blotches. It has twenty-eight 

 ridges, each of them having a row of small spikes. 



