unio. 153 



" Transactions " very properly wrote to Mr. Sardius for 

 proof of his assertion, and was informed, in reply, that it 

 depended on a certain Dane, named Henricus Arnoldt. 

 This account of the origin of pearls is on a par with the old 

 poetical fancy of their origin from drops of dew. We need 

 scarcely remind our readers that they are of the same 

 nature with the inner coats of the shell, and are abnormal 

 secretions of the mantle, composed of alternating and con- 

 centric layers of membrane and calcareous matter. 



The Pearl Mussel is an inhabitant of rapid streams flow- 

 ing from mountainous districts. Cumberland, Westmore- 

 land, and Northumberland, in the north of England, — the 

 streams of the hilly parts of Devon and Cornwall in the 

 south, — many of the rivers of Wales, both north and south, 

 — the streams of the Isle of Man, — the rivers flowing from 

 the Highlands of Scotland, and many Irish rivers, — are its 

 chief localities. Abroad it is found abundantly in Norway 

 and Sweden ; sparingly in mountainous districts of France 

 and Germany. 



Considerable difficulty has arisen from a statement by 

 the late Dr. Solander, the pupil of Linnams, that the Mya 

 pictorum of the British Islands was not the species so 

 designated by Linnseus ; a declaration either resulting from 

 his having only seen the much commoner U. tumidus (at 

 that time confused with it by the English conchologists), or 

 from his knowledge of the Linnsean types, a considerable 

 portion of which (yet not those agreeing with the synonymy) 

 is certainly of a form which we have not observed exactly 

 delineated among the European Uniones, but not unlike the 

 shell figured as M. pictorwm by Donovan (vol. v. pi. 174), 

 only broader in proportion to the length. Montagu having 



VOL. II. \ 



