ORDER TESTACEA. 125 
sometimes contains two or three supernumerary calcareous 
bodies. ‘The foot issues through the aperture on the side 
next to the mouth, where it is widest, and from the opposite 
end project the two tubes, which are united, and capable of 
enlarging themselves in every direction. 
The pholades inhabit canals which they excavate, some in 
ooze, and others in stone, like the lithodomi, petricole, &c. 
They are much sought for on account of their agreeable 
flavour. 
Several species are found on the coast of France: such is 
the Dail commun. (Pholas dactylus, L., &c.) 
TEREDO, Lin., 
The mantle extended in a tube much longer than the two 
small rhomboidal valves, and terminated by two short tubes, 
the base of which is furnished on each side with a strong and 
moveable kind of operculum or palette. These acephala, 
while quite young, penetrate and establish their habitations 
in submerged pieces of wood, such as piles, ships’ bottoms, 
&c., perforating and destroying them in every direction. It 
is thought, that in order to penetrate as fast as it increases in 
size, the teredo excavates the wood by means of its valves; 
but the tubes remain near the opening by which its entrance 
was effected, and through which, by the aid of its palette, it 
receives water and aliment. The gallery it inhabits is lined 
with a calcareous crust, which it exudes, and which forms a 
second kind of tubular shell. Itis a noxious and destructive 
animal in the sea-ports of Europe. 
Teredo navalis, L. This species, which is the most com- 
mon, and is said to have been introduced into Europe from 
the torrid zone, has more than once threatened Holland with 
ruin by the destruction of its dikes. It is upwards of six 
inches in length, and has simple palettes. 
Larger species inhabit hot countries, whose palettes are 
