jecls further in one valve than the other; which valve is 

 rather largeft, and receives tlie other within its margin, 

 particularly at the oppofite end from the hinge. In fome 

 both ends are truncated: colour dirty white, frequently 

 covered with a brown epidermis. Infide white, hinge 

 rough, flrong, inflefted, forming a deep cavity underneath 

 the margin. Length, from hinge to the oppofite margin, 

 a quarter of an inch, breadth half an inch, but ufually 

 much lefs ; though we have one Ipecnnen full three-quar- 

 ters of an inch wide. 



This fpecies is found on fome parts of the Cornijli coafl;, 

 and we have fcen it burrowed in lime-flone at Plymouth ; 

 but is n'ofl commonly met Vv'iih at the roots of Alg(Z, 

 not unfrequently on many parts of the coafl of South De- 

 von, as well as at Ilfracomb in the north of that county : 

 and we have received it from Wales. 



It is readily diflinguifhed from the young of the M. ru- 

 go/us by the larger end being truncated, and not rounded, 

 and by the valves being unequal. 



Crista Galli. Mytikis Crida Galli. Lin. Syji. p. lisr,. 



Ginel. Syft. p. 33,i0. 1. 

 Chem. Conch, viii. t. 75. f. 6S3. 6S4. 

 Id. t. 73. f. 615—GnaIt. t. 104. f. E. 

 Turt. Lin. iv. p. 2S9. 



M. with a rud?, rugged, compreffed fhcll, varying fo 

 much in Ihape as not to form any fixed charaQer : colour 



opaque 



