152 UNIONIDiE. 



left there by the flood.* Mr. Wilson of Warrington, in 

 Loudon's " Magazine of Natural History 1 '' for June, 1830, 

 says they are taken in the upper part of the Conway, near 

 Llanrwst, but the search is very precarious. He mentions 

 a Scotch pearl half an inch in diameter. In Scotland, the 

 Tay was the seat of a pearl-fishery, extending from Perth 

 to Loch Tay. "It is said,'''' writes Captain Brown, " that 

 the pearls sent from thence to London, from the year 1761 

 to 1764, were worth ten thousand pounds sterling; and it 

 is not uncommon at the present time to find pearls in the 

 Teith and Tay worth from one to two pounds each." The 

 variety Roissyi of this Unio was formerly much sought for 

 in the river near Braddan, in the Isle of Man, on account 

 of its pearls. 



In the ninth volume of the " Philosophical Transactions" 

 (1674) there are two letters from Hamburgh, by the 

 learned Christophorus Sardius, concerning the origin of 

 pearls. " The pearl-shells in Norway and elsewhere,' 1 

 writes this author, " do breed in sweet water. Their shells 

 are like to those which are commonly called mussels, but 

 they are larger. The fish in them looks like an oyster, but 

 it produceth a great cluster of eggs like those of era-fishes, 

 some white, some black (which latter yet will become 

 white, the outer black coat being taken off). These eggs, 

 when ripe, are cast out, and being cast out they grow, and 

 become like those that cast them. But sometimes it hap- 

 pens that one or two of these eggs stick fast to the sides of 

 the matrix, and are not voided with the rest. These are 

 fed by the oyster against her will, and they do grow, ac- 

 cording to the length of time, into pearls of different big- 

 nesses, and imprint a mark both in the fish and the shell by 

 the situation, conforming to the figure." The editor of the 



* Brit. Zool. iv. p. 80. 



