b. 



36 



The ovalis and margaritifera rarely if ever inhabit the 

 fame waters ; this being found only in the flow rivers, 

 and never in rapid torrents. 



The large and thick variety has, we underftand, been 

 alfo feparated by fome conchologids, and called Mya 

 folida ; but certainly without foundation; for tliere is no 

 leading character of dillinciion ; the fliape, hinge, teeth, 

 and every other part is the fame; and the only difference 

 is in the fubftance of the fhell, a circumflance not alone 

 fufficient to admit of its being a dillin61 fpecies. 



This very ftrong variety is not uncommon in the Avon, 

 that runs through the north of Wilt/hire and SomcrfetJJiirc, 

 inhabiting the deeper parts of the river. 



PiCTORUM. Mya P!6lorum. Lin. Syfi. -p. \\\2. 



Gmcl SyjL p. 321S. 

 Chem. Conch, vi. t. 1. f. 6. 

 Tiirt. Lin. iv. p. 175. 

 Shrcet. Flufscon. t. 3. f. 2. t. 3. f.45.— t. ■}. f.i:. 



M. with a fub-oval, fub -arcuated fliell, moderately 

 thin, of an olive-green colour, fometimes darker at one 

 end, inclining to dufky ; wrought with concentric wrin- 

 kles : beak or umbo placed near to one fide ; hinge nearly 

 ilrait, from which it declines alike to both ends, which 

 are equally rounded : the front margin either ftraight or a 

 little indented. Infide glofly, fmooth, pearly; in each 



valve 



