308 THE BRITISH NATURE BOOK 



preys upon other shellfish, drilling a hole in its victim's shell, and then, thrust- 

 ing its toothed tongue through the orifice, devours it at leisure. 



4. The Eed Whelk (Fusus antiquus) is larger than Buccinum, is iron-red in 

 colour, and is often sold for food. 



5. The Cowry (Cyprcea europea). The living Cowry presents a very dif- 

 ferent appearance from the shells so plentiful on our shores, for its mantle 

 almost entirely enwraps the shell, on the upper part of which you may see 

 a pale streak showing where the edges of the mantle met in the days when it 

 was alive. The shell is slightly flesh tinted above (sometimes with three 

 chocolate blotches), and ornamented by fine transverse ribs. 



6. The Smooth Margin Shell (Erato lavis] is smaller and has the lip curved 

 outward (instead of inward, like the Cowry), forming a distinct margin. It 

 is white and smooth. 



7. The Periwinkle (Littorina littorea) needs no description, being familiar 

 both to sight and taste, for this is the species so often used for food. 



8. The Dog Periwinkle (L. rudis), which is slightly larger and has a stouter 

 shell, and a deep purplish colour, though almost as common, is not edible, 

 for the reason that it retains its eggs inside its shell until hatched, and this 

 makes it very gritty. 



The small red or yellow shells found amongst the periwinkles belong to a 

 variety of the same species (L. littorea). 



9. The Purpura (Purpura lapillus), or PURPLE, is a form of Limpet, but its 

 shell is not unlike the Dog Periwinkle in shape ; indeed it is often known as 

 " DOG WINKLE." It has an operculum, unlike the limpets, and when disturbed 

 exudes a purple liquid, from which the famous Roman purple dye was obtained. 

 This is contained in a small sac, and is at first white, but changes colour rapidly 

 on exposure to light. 



The shell is white, with two or three bands of yellowish brown. The eggs 

 are fastened down to stones or little stalks. The Purple drills holes in other 

 shells and devours the inmates. 



10. The Wentletrap (Scalar ia communis) is sometimes called the " STAIR- 

 CASE SHELL," the ridges that run round it being not unlike a circular staircase. 

 It has a beautiful white colour. 



11. The Common Limpet (Patella vulgata) needs no description, but 

 is of great interest from various points of view. It can recess the rock on 

 which it rests so as to form a shallow pit in which the edge of the shell 

 fits neatly. This it does by scraping away the rock with its tongue (radula), 

 armed with its 2,000 teeth ; and the sound of the scraping can actually be 

 heard on a still day, when the rocks are out of water. After grazing on its 

 vegetarian diet at night it returns to the same spot for the day, settling 

 itself down, so to speak, upon its bedplate ! 



It has a broad foot, which exudes a thick glue, by which it literally sticks 

 itself to the rock (and not by suction, as is so often imagined). 



12. The Key-hole Limpet (Fissurella grceca] belongs to deep water, but 



