THE PINNA 57 



fish comes swimming past a pinna, and catches 

 sight of its gaping shells, it is almost sure to 

 venture in between them. Then the shells close 

 tightly, and it finds itself in a prison from which 

 there is no escape ; and very soon it is killed and 

 devoured. 



In colour, the shells of the pinna are very pale 

 brown, and a number of ridges run down it from 

 the smaller end to the larger. When the animal 

 is full-grown it is sometimes not at all easy to 

 see its shells, for they are covered almost all 

 over with barnacles and the tubes of sea-worms. 



