OTHER BIVALVE MOLLUSKS 105 
wood for food, but simply for the fun of the boring. 
The young of this mollusk, like those of many 
others, are free swimmers, quite unlike the par- 
ents. After a brief and sportive life in the water 
he finds a post or a floating piece of 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 undis- 
turbed wood. Thus it 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. They 
gape widely at both ends. The front of the shells 
is very beautifully sculptured, though the mark- 
ings are often so fine that a microscope is needed 
in examining them. ‘There are also two oar- 
shaped, shelly appendages, which close the exter- 
nal 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. 
Xylotria stutchburryi, Jeff., the Little Teredo, 
has a very small shell, of which the valves are 
white and triangular, while the pens are minute 
and club-shaped. 
This closes our descriptions of the two-valved 
mollusks. Very much concerning the details has 
been left unwritten, and for every observer there 
remain plenty of interesting facts, which are only 
waiting for some discoverer. 
