BRANCIIIFEROUS MOLLUSCA. 287 



but you may rely upon it that it could not be done, or done 

 only with a few, and to a very partial extent. A discovery 

 of M. de Freminville, quoted in Beudant's support, does not 

 more than vindicate my caution. This zealous and intelli- 

 gent naturalist, in a letter to Brongniart, says, " The weak- 

 ness of the waters of the Baltic Sea is still more perceptible 

 in the gulf of Livonia than any where else : it is such that 

 the mollusca of fresh water live there very well, and I have 

 found upon the shore Unios, Cyclades, and Anodontae living 

 pile mele with Cardia, Tellines, and Venus, — shells which 

 usually inhabit the saltest waters."* This is not exactly 

 the case ; there are species in all these genera which are 

 littoral, and do not dislike a diluted water. Mr. Garner 

 made experiments more conclusive than those of Beudant, 

 and I have no doubt of the soundness of his conclusions : — 

 " It would seem from this," he says, " that although perhaps 

 some of these animals may bear a slight change as to the 

 freshness or saltness of the water (and perhaps those species 

 inhabiting estuaries do so more than others), yet this capa- 

 city must be very limited. The Cardia, Mactrse, Amphi- 

 desmae, &c., found in marshes on the coasts, become diseased 

 and die when the water becomes concentrated by evaporation, 

 or when it loses its saltness by mixture with fresh. The 

 Mytili found in fresh water docks, are probably fresh water 

 species brought from foreign rivers, and which, perhaps, have 

 survived their immersion in salt water during their voyage, 

 by having kept their valves constantly closed ; some species 

 of Mj'tilus are known to inhabit fresh water. It appears 

 certain, that in those rivers where the Uniones, Anodontae, 

 and Cyclades abound, they cease to be found where the water 

 becomes salt."-}- 



But one geo-conchologist, at least, would have us to carry 

 our credulity a little further than even M. Beudant. I have 

 abeady told you that the common people of Barra believe 

 that their sandlo%dng and foodful cockles are born and bred 

 in the fresh springs of their hills, and come down to the 

 sea to receive the virtue that makes them so large and so 

 savoury. ;J: Our savant reverses the fable ; and he finds the 



* Jouni. de Physique, Ixxxix. p. 80, 



t Charlesworth's Mag. N. Hist. iii. 302-3.— In tlie "British Molhisca " 

 of Messrs. Forbes and Hanlcy, some facts corroborative of Mr. Garner's 

 views will be found. — Sec in })articular, vol. i. 172. 



^ Buchanan, in his history of Scotland, tells the tale, " On the north 

 side of Barra, one of the Western Isles, stands a verdant hill, from whose 

 summit springs a fountain of clear water, the source of a river, which 

 carries along with it to the neighbouring sea, certain small, but unformed 

 animalcula, which appear in part, but indistinctly, to be a species of shell- 



