TEREDO. SHIP-fFORM. 131 
difty white, rounded at the larger end, sliglitly truncate and 
a little angular at the other, finely striate concentrically, 
and crossed with minutely fine longitudinal lines; inside 
riot very smooth, with the margin uneven : hinge not cen¬ 
tal; in one valve two teeth, large, and distant; in the 
other a large triangular cloven tooth, with a smaller one 
«ar it: length half an inch; breadth something more. 
In the Firth of Forth: very rare. 
TEREDO. SHIP - WORM. 
Ml 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, i.s the lirst naturalist who has pointed out to our at- 
t ation the structure of the hemispherical valves which 
terminate the larger end of the cylindrical tube. Every 
Liajogy, in comparison with other genera of a similar 
structure, induces us to consider these valves as primary 
cjgans, and the tube with its various appendages as merely 
accessorial. Like the Pholos tribe, to which they seem to 
Ip most allied, they are furnished with distinct valves con¬ 
futed by a moveable hinge, and furnished with correspond¬ 
ing teeth. T lie tube appears to be a mere calcareous se- 
nedon, for the purpose of securing the animal a lubricous 
passage, and probably defensive against the rough surface 
o: occidental 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, appears to 
kin the frontal opening of the primary valves ; as in most 
eftne specimens which we have examined in a fresh state, 
toe to 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- 
Ued in shape the Anpmia Cepa. This mass was sufficiently 
Concave to Cover the valves, defended from its action bv a 
K peculiar 
