112 
TEREDO. 
(Plate XXII. Fig. 4.) 
Shell univalve, tubular, tapering, flexuous, pene- 
trating wood. One end is closed by two hemi- 
spherical, and the other by two lanceolate valves. 
It has been doubted whether the Teredines 
ought not to be considered as multivalve shells, 
rather than among the most simple of the univalves. 
The small valves which are attached in pairs to 
the fore and hind part of the animal are purely 
testaceous, and as necessary to the habits of the 
worm as the tube in which he dwells. The ante- 
rior hemispherical valves are placed at an angle, 
and furnished internally with a long flat and curved 
tooth, probably intended to strengthen the mol- 
luscous head on which this curious boring instru- 
ment is fixed. The smaller end of the tube, in 
which the lanceolate pair are situated, remains at 
the surface of the perforated wood, and the little 
valves are used as flood-2;ates to admit more or less 
of the water according to necessity. There appears 
