561 



Mytilus rugofus, Donax Irus, Venus p erf or ans, andfomc 

 others, are deftroying the hardeft Hme flone ; the Pho- 

 ladei are performing fimilar works, aihgned by nature? 

 on fofter fubftances, fuch as chalk, indurated clay, and 

 wood, which in Hke manner are perforated by fome fol- 

 vent power ; not by the thin, fragile fliells, that cover 

 fuch animals, as fome have errorieoufly afferted, and is 

 too generally credited. All thefe become fixed in their 

 cells for life, for as they ent'er in the moft minute ftatc, 

 the excavations are conic, with the fmall end outwards, 

 fo that the fliells are as it v/ere becorrie enclofed. 



It is moft probable, the young of thefe, and other per- 

 forating Afcidia, that drill the fmall round holes fo fre- 

 quently obferved on fhells : and not the Trochi, which 

 are incapable of fuch works. 



Don. Br. Shells, iii. t, 73. Margaritife- 



Under the article Pearl, in the Encyclopcedi.i Britan- ^r, 



mca, we find the following note : 



" There has been in thefe parts, ( i. e. at Perth, in 

 '• Scotland,) a very great fifhery of Pearl, got out of the 

 frePii-water Mufies. From the year 1761 to 1754, 

 " 1O5OO0/. worth, were fent to London, and fold from 



C c c c " lOi. to 



of Government. A coating ot p :)uii ;eJ iiint, or glafs, lail on t'inber with a 

 firm cement, v.-oulU eRcdlually picfcrve it trom the calamitous ravages of the 

 Teredo navalis, and other aiiimals of Cmilar habits. 



