m 



it as a variety, of that fliell ; and we are told his fliell came 

 from Sweden ; from which it may be inferred that the north- 

 ern feas are moft congenial to the growth of this fpecies. 



3tacnaLis, IMytilus Stagnalis, Gmel. Sjjst. p. 336'i. 



Schroct, Flusconch. t. 1. f. 1. 

 Br. Miscel. i. t. 15. 



It will be obferved Gmelin on the authority of Schroeter 

 has defcribed a fliell under this title, which he likens to M. 

 cygneus, differing only in being larger and lefs convex. We 

 alfo on the authority of Mr. Sowerby give it a place as 

 Englif}}, but not without very confiderable doubt of its being 

 diftindl from M. cygneus. The fliell which was found by a 

 friend of Mr. Sowerby by the fide of the lake in iiCiezt; garden, 

 differs from Schroeter's fliell in that particular which was 

 fuj^ofed mofl eflential to its difiinftion from cygneus, for 

 inflead of its being lefs convex, it is admittrd to be more 

 convex than cygneus. Upon the whole therefore, when a 

 confiderable number of thefe fhells are examined, wc find 

 thofe gradations which connedl thefe two fuppofed fpecies, 

 and no criterion of diflinclion remains as fpecifically cha- 

 ra^teriftic. 



There is fcarcely perhaps a fpecies of Tejlacea if the ex- 

 tremes, or two fpecimens moft diflimilar were alone exa- 

 mined by the moft able conchologift, but what would be 

 pronounced diftin6l ; whereas could he have confulted 

 the intermediate fliades, and gradations, his opinion would 

 have been entirely changed. ,y 



