312 THE BRITISH NATURE BOOK 



8. The Radiated Scallop (P. radiatus) is rather rare, but may be known by 

 the six or seven ridges running down it. It is also a variable species, generally 

 reddish brown spotted with white. 



9. The Hunchback Scallop has one of its valves so much deeper than the 

 other that it has a hunch-backed appearance. It changes its shape very much 

 as it grows, so that its shells might often be taken to be injured specimens. It 

 is white, with reddish mottles. 



10. The Sunset Shell (Psammobia ferroensis). Very common in some 

 localities, but entirely absent in others. Its name is given on account of the 

 beautiful colouring of the inside rosy pink, orange-yellow, or crimson-streaked, 

 suggesting a sunset sky. The outside is white. There are four British species. 



n. The Wedge Shells (Donax) are very similar, but the hinder end is wedge- 

 shaped or pointed instead of round. They are similarly but not so strongly 

 coloured. The Common Wedge (Donax anatinus) is the most familiar. 



12. The Gaper (My a arenaria). So called because the shells are open at 

 the top, through which the siphon tubes project. In some parts of the country 

 it is used for food, the popular name being " OLD MAID." 



13. The Piddock (Pholas dactylus) is 3 to 5 inches long, with a white shell, 

 thin and delicate, covered in front with rasp-like ridges ; the two valves not 

 united by a hinge. There are, besides, three small additional valves to be 

 seen on living specimens. 



14. The Little Piddock, RED-NOSED BORER (Saxicava rugosa), has a shell 

 much distorted and varied in shape. In an early stage it is symmetrical, 

 having two minute teeth on each valve ; but these are absent in older specimens. 

 The shell is covered with ridges and wrinkles. The ends of the siphon are crimson, 

 and may be seen sometimes protruding from a cliff face in which the borers 

 have lodged themselves. 



[The empty shells of these two species (Nos. 13 and 14), and of other allied 

 ones, may be found near limestone or chalk cliffs, and if you examine the rocks 

 at low tide you will find them perforated by large or small oval holes, several 

 in close proximity, the work of these extraordinary shellfish. How they do it 

 is uncertain probably by taking a firm purchase with their foot and twisting 

 the shell half-way in one direction, and then reversing the motion. When the 

 burrow is choked with material thus excavated, the Pholas clears it with a jet 

 of water from its siphon. In this way this mollusc is doubtless responsible 

 for a considerable share in the undermining of our sea cliffs, and may even 

 have helped in bygone ages to cut the neck of land that joined this country to 

 France, thus making Great Britain an island.] 



15. The Ship Worm (Teredo navalis) is in reality a mollusc and a bivalve, 

 though it looks like a worm, about as long and as thick as a pencil. The two 

 valves are very small, and at the head end of the body ; they used to be con- 

 sidered jaws. It bores into timber, and can do much harm to wooden hulls 

 and pier piles, in which it burrows its chamber, lining it with a shelly coating. 



16. The Razor (Solen siliqua). These are very familiar and need no de- 



