24 THE SEA-SHORE 



in the least, and they devour so many of both 

 these kinds of periwinkles that i is quite a wonder 

 that any are left alive. 



PLATE IX 

 THE PURPURA (5) 



In size and shape this very common creature 

 is rather like the dog periwinkle. But its shell 

 is white in colour instead of bluish black, and 

 generally has two or three bands of light yellowish 

 brown running round it. You may often find it 

 crawling about on the weed-covered rocks when 

 the tide is out. 



The purpura is quite a famous creature, because 

 of the use which was made of it by the ancient 

 Romans. I daresay you know that in days of 

 old the colour of purple was very highly valued ; 

 and among the Romans only members of the royal 

 family were allowed to dress in purple garments. 

 Now this purple dye was obtained from the 

 purpura. Inside its body this creature has a 

 little bag which contains about a drop of a thick 

 white liquid, rather like milk. Certainly it does 

 not look in the least like purple dye. But if you 

 were to squeeze it out on to a sheet of white 

 paper, and to place it in the sunshine, you would 

 very soon see that it was changing colour. In 



