43 



convex, moftly of a fub-oval form ; but rifes high at the 

 umbo, where ii proje61s beyond the margin or covimijfare ; 

 the beak is fmall, placed nearly central, and does not 

 turn to either fide. In the broader fpecimens the hinge 

 is placed nearer to the larger end; fuch are not in general 

 fo uneven and rugofe as thofe of a more fub-orbicular 

 fhape ; but all are more or lefs finuous and indented ar. 

 the margin. Infide white: hinge furnifhed with a broad 

 fub-triangular tooth in each valve, hollowed in the mid- 

 dle, projecting horizontally inwards, much like the pU' 

 befcens : thefe teeth, like the two preceding fpecies, cover 

 each other when clofed, and by which the valves are con- 

 nefted with a cartilage. This fhell, which has fomething 

 of the habit of the two preceding fpecies, is much more 

 convex than the prcetenuis, and the tooth not fo long and 

 rounded; it differs alfo from xhe pubefcens in the fhape of 

 the tooth, and in not being truncated ; and from both in 

 its rugged and diflorted fhape. 



We firfl noticed this fpecies at Falmouth, amongfl the 

 fand dredged from the harbour for manure, and have 

 fince found it lodged in hard lime-flone at Plymouth, into 

 which it had bored like the Pholas ; probably the occa- 

 fion of its diflorted growth. It is alfo found on other 

 parts of the coafl of South Devon, but not plentiful. 



The largefh fpecimen we have met with is not above 

 three-quarters of an inch long and an inch wide ; others 

 are as long as they are broad. This and the two pre- 



G 2 cedinsf 



