212 BY THE DEEP SEA. 



away from our illustration of the Purple (Purpura lapillus], 

 on page 208, to which we must now hark back. The Purple 

 is often known as the Dog Winkle. It abounds upon the rocks 

 between tide-marks, whence it may be picked without the 

 formalities necessary in the case of the Limpet. It comes off 

 easily, for its foot is small, but the moment it is disengaged 

 from the rock it retires into its shell and closes its door. Now 

 apart from the difference in the shape of the shell, here is 

 another departure from molluskan arrangements as illustrated 

 by the Limpet. It is called an operculum (Latin, a cover or 

 stopper), and is so attached to the foot, that when the Purple 

 withdraws from public view this comes last, and fits the 

 mouth of the shell so accurately that there is no getting inside. 

 In this case it is a homy oval disk, but in some species it is 

 strengthened by the deposit of layers of shelly matter until it 

 becomes of considerable thickness and quite stony. If we 

 mark our disapproval of the Purple's lack of courtesy in 

 slamming his door in our face, by pushing against his door, 

 he retaliates by exuding a purple fluid, which is said to 

 permanently dye fabrics a similar hue. The Purple is riot 

 a vegetarian like the Limpet. His mouth forms a fleshy 

 proboscis, which contains a marvellous boring apparatus 

 the modified tongue. Often you may pick up bivalve shells on 

 the beach, of which one has been pierced with a very clean 

 and smooth round hole near the beak. If you did not know 

 otherwise, you might suppose that this was the work of a 

 person who desired to make a shell-necklace or other orna- 

 ment, and had bored this hole with the greatest of care, and 

 then had unfortunately dropped it on the beach. The truth 

 is, it is the work of the Purple, or some other carnivorous sea- 

 snail. He has the reputation of being very destructive to 

 mussel-beds, by boring these workmanlike holes in their shells, 

 and literally eating the poor mussel out of house and home. 

 That is the style in which the Purple gets his living ; but he 

 has a Nemesis in the shape of the Star-fish, and I have seen 



