66 PHOLADIDiE. 



the way, it can change its course, and work round the ob- 

 stacle. The tube is the lining of the tunnel in which it lives 

 and conducts its operations. The destructive character of 

 its work is well illustrated by an instance narrated by Mr. 

 Thompson. A piece of pine wood nine inches in diameter, 

 after having been employed as a pile for five years and a 

 half, was so reduced by the perforations of Teredines^ as to 

 contain not more than about an inch of solid timber in any 

 j)art, and in several places was completely bored through. 

 This pole was placed fifteen feet below high water-mark, 

 and left dry only during low water at spring-tides. ISIon- 

 tagu remarks that sound piles will be found completely 

 perforated by Teredines after four or five years submer- 

 gence. Well might Linnseus style it " calamitas navium !" 

 Remedies and preventives of many kinds have been pro- 

 posed, most of them various ways of preparing timber. It 

 is doubtful whether any have proved successful, though it 

 has lately been asserted that creasoted timber is not touch- 

 ed by the ship- worm. Baster, who published a paper on 

 the subject in the "Philosophical Transactions" for 1739-40, 

 mentions, that most of the proposed specifics against the 

 Teredo in his day were mercurial ; but states they had 

 proved of no use, and recommends varnishing the wood. 

 The only efiicient protection for piles seems to be the stud- 

 ding of their surface closely with broad-headed nails. 



1. Teredo norvagica, Spengler. 



Valves : — Body or fang-shaped portion of moderate length, not 

 slender and produced ; auricle seated on the posterior shoulder, 

 not dilated nor defined externally ; internally parted off by a dis- 

 tinct carina ; its base scarcely, if at all, lower than that of the 

 projecting front triangle. Subumbonal blade rather wide, pre- 

 senting its broader surface to the inner disk. 



Pallets testaceous, flask-shaped, not forked at the base. 



