TEREDO. SHIP-WORM. 181 



dirty white, rounded at the larger end, slightly truncate and 

 a little angular at the other, finely striate concentrically, 

 and crossed with minutely fine longitudinal lines; inside 

 not very smooth, with the margin uneven : hinge not cen- 

 tral ; in one valve two teeth, large, and distant ; in the 

 other a large triangular cloven tooth, with a smaller one 

 near it : length half an inch ; breadth something more. 

 In the Firth of Forth : very rare. 



TEREDO. 



Shell with two primary hemispherical valves, 

 each of them furnished with a long incurved tooth ; 

 and attached at the posterior side to a long cylin- 

 drical testaceous tube. 



Montagu, whose opportunities and whose accuracy of 

 discrimination led him to a close examination of this ge- 

 nus, is the first naturalist who has pointed out to our at- 

 tention the structure of the hemispherical valves which 

 terminate the larger end of the cylindrical tube. Every 

 analogy, in comparison with other genera of a similar 

 structure, induces us to consider these valves as primary 

 organs, and the tube with its various appendages as merely 

 accessorial. Like the Pholas tribe, to which they seem to 

 be most allied, they are furnished with distinct valves con- 

 nected by a moveable hinge, and furnished with correspond- 

 ing teeth. The tube appears to be a mere calcareous se- 

 cretion, for the purpose of securing the animal a lubricous 

 passage, and probably defensive against the rough surface 

 or accidental collapse of the wood. The formation of this 

 secretion, which seems to have a solvent power over the 

 resin of the wood, and perhaps the fibre itself, appeal^ to 

 be in the frontal opening of the primary valves ; as in most 

 of the specimens which we have examined in afresh state, 

 there was found at the head of this opening, a thin soft 

 pulpy hemispherical mass, of a chalky white color, which 

 hardened upon exposure to the atmospheric air, and resem- 

 bled in shape the Anemia Cepa. This mass was sufficiently 

 concuve to cover th e valves, defended from its action bv a 

 R peculiar 



