> T C 



3Q 



8. 



M. with a fub-pellucid, fub-orbicular fliell, of a yel- Suborbicuj. a 

 lowifli-white colour, frequently covered with a brown ^' 



epidermis ; faintly ftriated tranfverfely, fomewhat glolfy ; 

 margin oppofite the hinge nearly ftrait; fides nearly equal, 

 rounded : hinge central : beak fmall, pointed, turning 

 to one Ude : in one valve a fmsfle tooth immediatelv 

 under the beak, locking into a double one in the oppofite 

 valve ; with a laminated tooth behind the beak in each, 

 fomewhat remote. Infide gloITy-white: valves (liut clofe. 

 Length rather exceeding three-eighths of an inch; breadth 

 half an inch. 



We firft difcovered this fpecies in hard lime-ftone at 

 Plymouth, fragments of which were thrown upon the 

 beach perforated in all directions ; the entrance of thefe 

 excavations were much fmaller than the fhell, fo that it 

 muft have entered in a younger ftate ; and from v»'hich 

 it never could recede. It is fometimes dredged up in 

 Salcomb-bay, detached from any other fubflance, fo that 

 it does not feem to be a Borer in all fituations : perhaps it 

 does not enter any thing but lime-ftone, which is not to 

 be found in this lalt place. 



This fhell is fo much like the Cardium corneum in 

 fhape, that it might readily be miftaken for a variety, ex- 

 cept attention is paid to the hinge, and that this is marine, 

 whereas the otlier is only found in frefh-water. A variety 

 is highly gloifed, with a refplendent pearly hue. 



Mya 



