BIVALVES. 



4i7 



a delicacy, and many species are highly phosporescent. In the second family the 

 ship-worm {Teredo) is only too well-known on account of the amount of damage it 

 does to submerged timber. It matters not whether it be oak, pine, teak, or 

 mahogany which it attacks, soon the timber is riddled through and through, and 

 rendered useless. In former times, before the invention 

 of copper-sheathing, immense damage was inflicted upon 

 shipping, and the piles of piers and harbours were con- 

 stantly having to be renewed through the ravages of 

 this pest. The Dutch have been great sufferers, and 

 at one time such depredations had been made on the 

 piles which support the dykes of Zealand and Friesland 

 as to threaten them with total destruction. The animal 

 is practically nothing more than an extremely prolonged 

 Pholas. The siphons are of immense length, in some 

 cases from two to three feet long, united except towards 

 the ends. On the contrary, the body itself containing 

 the principal viscera is small, and protected by a 

 globular, bivalved shell, open both in front and behind. 

 The gills are narrow, elongate, and prolonged into the 

 branchial siphon. The siphons secrete a shelly lining 

 to the burrow, and at the point where they separate 

 there are a pair of calcareous plates, or pallets as they 

 are termed, probably used as a means of defence, in 

 closing the tube after the siphons have been retracted. 

 Ship- worms generally bore with the grain, only turning 

 aside to avoid a knot or any other obstruction; and 

 although their burrows are almost touching, they 

 seldom appear to run into one another. The animal 

 does not feed upon the wood it excavates, but ejects it 

 in small particles through the siphon. The foot is 

 probably the burrowing organ, but the method of 

 excavation is still imperfectly understood. Hyperotus, 

 Nausitoria, Xylotrya, and Cyphus are other forms of 

 Teredinidce ; the last named constructing a strong, 

 shelly tube, sometimes a yard long, and two inches in 

 diameter, in which the creature lives buried in the sand. 



Suborder Anatinacea. 



This, the last suborder of the Eulamellibranchiata, 

 contains thirteen families of which only a few are of , 

 general interest. Of the Pandoridce, the typical Pan- 

 dora is distinguished by its compressed, internally pearly shell, which is sometimes 

 semi-lunate in form ; the right valve being flat, and the left somewhat convex. 

 P. inonquivalvis is a common British species. In Myadora, an allied genus, the 

 left valve is flat, and the right convex. The species of the third genus, Myochama, 



vol. vi. — 27 



