MOLLUSCA. 193 



Hessling was also directed to examine whether the 

 artificial propagation of Unio margaritiferus, with a 

 view of producing pearls, is practicable. The results 

 of his labours were published in 1859 at Leipzig in 

 an 8vo volume of 376 pages, entitled, " Die Perl- 

 muscheln und ihre Perlen," etc., to which interest- 

 ing work I refer those who would undertake similar 

 experiments in England. 



Two descriptions of pearls are collected and 

 turned to account in Wales. They are known in 

 England as the " Conway river pearls. " The first, 

 which are of little value, are taken from the 

 common mussel (Mytilus edulis), at the mouth 

 of the river Conway. The others, which are fre- 

 quently very fine, are taken further up the stream, 

 from the shells of Unio margaritiferus. As early as 

 1693, a paper was published in the "Philosophical 

 Transactions/' by Sir Robert Redding, who states 

 that at that period an extensive fishery for these 

 pearls was carried on by the natives who lived near 

 the rivers in the west of Ireland, " Although, by 

 common estimate," says the author, " not above 

 one shell in a hundred may have a pearl, and of 

 those pearls not above one in a hundred be tolerably 

 clear, yet a vast number of fair merchantable pearls, 

 and too good for the apothecary, are offered for sale 

 by those people every summer assize. Some gen- 

 tlemen make good advantage thereof, and myself 



