MOLLUSCA. 



173 



towards their outer edges, are the chosen residence of millions 

 of mussels, forming continuous beds, from whicli the people 

 of the village procure an abundant supply, and 

 where boats are sometimes filled with mussels 

 for the Belfast market. By crossing the narrow 

 neck of land which separates the loughs of Belfast 

 and Strangford, we come at once upon a wide 

 extended beach of sand. Here the Limpets have 

 disappeared — the Mussels abound no longer, and 

 their place is more than suj)plied by multitudes 

 of the common Cockle, v/hich alike farnish food 

 and occupation. 



Among the MoUusks of the present class, arc 

 those which possess the art of boring into hard sub- 

 stances, and living in the excavation thus formed. 

 We have dug out of indurated clay, so hard as 

 to make onr progress in it a work of labour, 

 perforating bivalves of two genera (Pholas and 

 Venerupis). Some even bore into the solid lime- 

 stone rock, and the piers and breakwater at 

 Plymouth, which arc formed of this material, 

 bear evidence of their powers. Perhaps none of 

 these animals is so noted for its ravages as the 

 Teredo (Fig. 161), which Linnseus emphatically 

 termed " calamitas navium." " They are now 

 common in all the seas of Europe, and, being gifted 

 with the power of perforating wood, they have 

 done, and continue to do, extensive mischief to 

 ships, piers, and all submarine wooden buildings. 

 The soundest ami hardest oak cannot resist them ; 

 but in the course of four or five years they will so 

 drill it as to render its removal necessary, as has 

 happened in the dockyard of Plymouth. In the 

 year 1731 and 1732, the United Provinces were 

 under a dreadful alarm, for it was discovered that 

 these worms had made such depredations on the 

 piles which support the banks of Zealand, as to pj ,g,^ 

 threaten them with total destruction, and to claim terido. 



half a mile distant. No instance of disease from this diet occurred; and, 

 during that summer, the poorer classes in the village appeared quite .-is 

 healthy as in other years, though mussels formed the chief part of their 

 food." 



