229 
TEREDO, Linn. &c. 
Gen. Cusr. Bivalve, gaping; back and posterior 
side closed by membrane or shelly valves ter- 
minating an accessory shelly tube. Hinge with 
one tooth in the right valve. <A long free 
process arising from the beaks contained in 
each valve. 
Ee 
Tue principal valves are longer than broad, striated, 
gaping at -both sides and at the back; in the posterior side 
of each is a deep rectangular sinus; in the anterior side is 
a corresponding small rounded sinus; the front is lanceo- 
Jate, with an internal tubercle at the extremity; one of 
the accessory valves lies over the beaks and is lobed; 
another is trapezoidal, covering the sinus at the posterior 
side, it has a line down the middle where there may pos- 
sibly be an opening, or it may indicate two valves. The 
membrane which covers the shell is extended over the 
anterior side, forming a taper tube many times longer than’ 
the proper shell, and strongly impregnated at a little dis- 
tance from the valves with shelly matter; in the extremity 
of this lie two spatulate valves, attached by muscles to the 
animal, and capable of closing the aperture, in which is 
placed a longitudinal septum ; this tube is slightly attached 
to a tortuous passage bored in wood by the animal, and is 
elongated and gradually increased in diameter as the 
animal recedes further into the wood. 
The resemblance between this Genus and several species 
of Pholas is remarkably strong; the species of Pholas nearest 
related to it are those which have one lobed accessory 
valve covering the beaks; these have also a tooth in the 
hinge close to the beak, so that there remains nothing ex- 
cept the greater proportional breadth (which makes the 
