40 THE SHELL-FISH OF THE COAST. 



against the rock in concentric lines. However this 

 may be, it is certain that the hole is very evenly 

 cut, and that it is increased in size in conformity 

 with the development within the rock of the animal 

 itself. 



A rather remarkable form of borer, which was 

 first detected within the shells of the oyster at 

 Tottenville, Staten Island, is the Diplothyra Smithii, 

 a very much smaller shell than either of the pholads, 

 and perhaps more nearly recalling the true ship- 

 worms. The latter (PI. 2, Figs. 4, 12, 13), by rea- 

 son of their depredations, are the most interest- 

 ing of the boring Mollusca. They are largely in- 

 habitants of the tropical waters, but have in the 

 timber of ships been introduced almost everywhere 

 over the wide sea. The body proper of this 

 singular creature is usually very small, but through 

 the great elongation backward of the siphons the 

 animal is made to appear worm-like (although it 

 has no near relation to the worms), and to attain a 

 length varying in the different species from one 

 to three or even six feet. The shell is compact, 

 ridged, and open at both ends, and only sufficiently 

 large to cover the anterior or body-portion, the 

 animal thus appearing naked. Beginning in very 

 early life, when frequently not over two weeks old, 

 and when only of about the sizeof theheadof apin, 

 the young ship-worm or Teredo puts itself to the 

 task of boring, selecting for its base of operations 

 all forms of wood or timber that may be immersed 

 in water, whether the belongings of siiips, dikes, 

 piles, or piers ; indeed, one or more forms even 



