TEREDO. SHIP - TVOPM. 
183 
pally from the primary valves, regarding them as corre¬ 
lative with all those shells which are furnished with a hinge 
connecting the valves by a cartilage ; at the same time 
taking into our view the peculiar formation of the lower 
accessorial valves, and the tube. 
1. Teredo n avails. Common Ship-worm* 
Home , in Philos. Transact. 1S06. pi. 12 and 13. 
Shell thin, brittle, semitransparent, white, covered when 
fresh with a dark brown or deep green skin, with a large 
circular opening in front: valves very convex, both sides 
tapering longitudinally, or from the hinge to the front 
margin, to an obtuse point, giving.thcm a triangular appear¬ 
ance ) on one side of each, close to the hinge, is a-some¬ 
what triangular projection, which is regularly but rather re¬ 
motely striate transversely ; behind this is a narrow space 
minutely and closely striate longitudinally in straight lines $ 
the remaining surface irregularly striate in a curved direc¬ 
tion: on the opposite side, close to the hinge, is a smooth 
rounded projection, defined on the underside by an oblique 
longitudinal ridge ; inside white, glossy, with a thick knob 
at the termination of the smaller end : hinge with a long 
deader curved tooth in each valve, placed interiorly as in 
thePholas,besides a tooth-like projection seated upon the 
hinge, which in one valve terminates in a small reflected 
lamellar point locking into the opposite valve : tube 
smooth, thin, taper, straight or a little flexuous, from a 
foot to two feet in length, lodged in wood, contracted in¬ 
ternally towards the smaller end, where the inhabitant is 
attached hv a strong muscle : at. this place it is furnished 
with two spoon-shaped valves, linear and somewhat flexu¬ 
ous at top, and dilated at the bottom, concave on the inside 
uith a rib down the middle, truncate at the end, for the 
purpose of closing up the orifice at pleasure, and containing 
the two terminal tubes of the animal: below these valves 
the tube is divided by thin close-set transverse circular 
partitions, ten or twelve in number, filling up about half 
the orifice and leaving a large oval opening ; and close to 
the end it is again crossed by a dissepiment, causing a dou¬ 
ble opening at the termination for the protrusion of the two 
tubes at the lower extremity of the animal : length of the 
r 2 primary 
