1/2 



Shell Life 



species tliat has caused so much damage and anxiety 

 to the Dutch. The Norwegian Ship - worm {T. 

 norvegica) is very similar to the last, but larger in 



all respects, the shell 



more solid and coarser 

 in its sculpture. The 

 'arofe pallets 



oval 



have 

 with 



Norwegian Ship-worm 



2, pallets; 3, part of sheath, broken 

 to show internal plates 



blades 

 squarish ends, con- 

 cave on the inner 

 side. Althouo'h found 

 all round our islands, 

 it is a local species, 

 and appears to con- 

 fine its attentions to 

 fixed timbers, and to 

 let floating spars and logs pass. The Guernsey 

 Ship- worm (T. 'pedicellata) is also very similar to 

 the Common Ship- worm, but much smaller in every 

 way ; probably, indeed, it is only the young condition 

 of a variety. Its chief claim to be considered distinct 

 lies in the shape of the pallets, which have long 

 stalks, a square blade, and an oval portion between 

 the blade and the stalk. It has been found in 

 submerged timber in several of the Channel Islands. 

 The Drifting Ship - worm {T. onegofara), although 

 occasionally found in fixed timbers on our shores, is 

 chiefly known to us as a common inhabitant of the 

 drifting logs and spars that come no one knows 

 whence, and get cast on our shores in stormy weather. 

 Full-grown specimens are intermediate in size between 

 T. naval'is and T. norvegica. There is an expansion 

 of the hinder margin of each valve known as the ear 



