Gapers^ Piddocks, and Ship-worms i 7 i 



but witliout any dorsal shield. Each valve is three- 

 lobed, and the hinder lobe is usnally spoken of as the 

 auricle or ear. The animal differs from the shell in 

 its shape, which is worm-like, and for the protection 

 of this part a chalky tube is secreted — of great length 

 in some foreign species, and extending to a couple of 

 feet in our own T. norvegica. At the mouth of this 

 tube the animal has developed a pair of accessory 

 valves (known as pallets) in the shape of paddles, 

 the handles of which are attached to tJie body, and 

 the blades serve to close uj) the tube when the 

 siphons have been withdrawn. They all burrow into 

 submerged vegetable substances, including all kinds 

 of timber, and are never found in rocks. They 

 appear to do all the boring by the action of the 

 small foot, though it is probable that the valves may 

 be used to enlarge and round off* the cell. The 

 burrows run with the grain, and consequently 

 parallel with each other. It is popularly supposed 

 that the Ship-worms destroy timber in this way to 

 serve as food, but though the excavated material is 

 passed out through the exhalent siphon it does not 

 appear that the animal derives any alimentary benefit 

 from it, but derives its nutriment fi'om the microscopic 

 life of the seas, j ust as the oyster and the cockle do. 

 The species are : — 



The Common Ship - worm {T. navalis), usually 

 about a foot long, sometimes as much again. The 

 shell is rather thin, and finely ridged. The pallets 

 have an oval blade, which is indented deeply at its 

 free end, glossy without, polished and flat within. It 

 is found in pine, elm, oak, and teak that have been 

 used for boat-building, piers, piles, etc. This is the 



