56 THE SEA-SHORE 



PLATE XX 



THE PINNA 



This is the largest of all the shell-bearing 

 molluscs which live in our British seas, for it 

 has been known to reach a length of nearly two 

 feet. It is found chiefly on our southern coasts, 

 and always lies upright, half buried in the mud 

 at the bottom, of the water, with its shells partly 

 opened. And it always fastens itself down by 

 a bunch of "byssus" threads, like those of the 

 mussel, which are so strong that it takes a very 

 hard pull indeed to tear them away from their 

 hold. 



In the British Museum you may see a pair of 

 gloves which have been made out of the byssus 

 threads of a pinna, and if these creatures were 

 more plentiful their threads would no doubt be 

 used in this way very largely indeed. 



Now why do you think that the pinna always 

 rests at the bottom of the water with its shells 

 partly opened ? 



Well, the reason is a very odd one. It is 

 setting a trap for fishes ! For fishes, as perhaps 

 you know, are very inquisitive creatures. They 

 always want to know all about everything, and 

 whenever they see a hole they think that they 

 must find out what is inside it. So when a little 



