557 
and boring marine animals. 
its habitation, the adductors perform a very essential part. 
The animal being attached by the foot, brings the anterior 
points of the shell into contact. The lateral muscles now 
contract, and raising the posterior extremity of the shell, 
press its operative part against the bottom of the hole ; and, 
the moment after, the action of the posterior adductor brings 
the dorsal margins of the valves into contact, so that the 
strong rasp-like portions are suddenly separated, and scrape 
rapidly and forcibly over the substance on which they press. 
As soon as this is effected, the posterior extremity sinks, and 
the stroke is immediately repeated by the successive contrac- 
tion of the anterior adductor, the lateral, and the posterior 
adductor muscles. 
The particles rubbed off, and which, in a short time, com- 
pletely clog the shell, are removed in a very simple manner. 
When the projected syphon is distended with water, the 
Pholas closes the orifices of the tubes, and retracts them sud- 
denly. The water which they contained is thus ejected 
forcibly from the opening in the mantle ; and the jet is pro- 
longed by the gradual closure of the valves, to expel the 
water contained within the shell. The chamber occupied by 
the animal is thus completely cleansed ; but, as many of the 
particles washed out of it will be deposited before they reach 
the mouth of the hole, the passage along which the Pholas 
projects its syphon is constantly found to be lined with a soft 
mud. 
As a British animal, I believe the Teredo to be nearly, and 
probably quite extinct. In the harbours of Falmouth and 
Plymouth, where, some years ago, it was so abundant, it is no 
longer to be found. In the Royal dock-yard at Devonport, 
mdcccxxvi. 3 A 
