TEREDO. S///P- WOEM. 1 83 



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 navalis. Common Ship-worm* 

 Home, in Philos. Transact. 1806. 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^them 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 

 slender curved tooth in each valve, placed interiorly as in 

 the Pholas, 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 by 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 

 witli 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 



