116 WEST COAST SHELLS 



that is known by the name of Xylotria setacea. 

 Try on, though it is commonly called the Teredo, or 

 Ship- worm. Its great end in life seems to be to bore 

 as long a hole as possible; not for the reason that it 

 desires the wood tor food, but simply tor the fun of 

 the boring. 



The young of this mollusk, like those of many 

 others, are free swimmers, quite unlike their adult 

 parents. Atter a brief and sportive life in the water 

 the little creature finds a post or a piece of floating 

 wood and begins to bore. As he advances, he lines 

 the hole with a tube of shell, and if he nears another 

 hole he turns to one side and bores on through un- 

 disturbed wood. The openings on the outside of the 

 wood, where the little creature entered, are so small 

 that they are hardly noticed, and so it often happens 

 that the timbers of a wharf may appear perfectly 

 sound, when in fact they are completely honey- 

 combed. 



The valves of the shell are at the very front of 

 the tube, and are nearly spherical in shape, though 

 they gape widely at both ends. The front ends of 

 the shells are very beautifully sculptured, though 

 the markings are so fine that a microscope is needed 

 in examining them. The creature also has two oar- 

 shaped, shelly appendages, which close the external 

 opening of the burrow, and perhaps perform other 

 duties. The globular shell of the Teredo is about 

 half an inch in diameter, and the pens or oars are 

 some two inches in length. 



To provide against the rapid destruction that is 

 wrought by the Teredo, many precautions are taken 



