CO^CHYL\/i—DITHYliA. 33. liJl 



Turton, Couch. Diet. p. 236. 

 Mus. nost. Western and Scotch coasts. 



Shell an inch long, and an inch and quarter broad, white 

 covered with a chesnut or olive skin, very slightly angular and 

 produced at the anterior side, with numerous regular equidistant 

 rounded transverse ribs, which grow fainter and indistinct towards 

 the sides, especially the anterior side, and having the interstices 

 smooth and broader than the ribs themselves : beaks somewhat 

 triangularly prominent pointed and slightly curved, with a heart- 

 shaped deep imfpres?ioB under them on the hinder side, and a 

 lanceolate one on the antei'roV side, both of them smooth; inside 

 glossy white or cream-color : hinge witii two strong teeth in each 

 valve. 



A suggestion has been hintetl to us that this species may be the 

 young of the Crassina sulcata, before the crenulations of the 

 margins show themselves : but we have both the sjiecies from the 

 size mentioned above to less than a quarter of an inch, and irt all 

 their stages of growth can readily distinguish the present specie^, 

 even T^ hen the valvds are shut close, by the flatness and sharpness 

 of the margin, which in Crassina sulcata is always obtuse. 



=^=1^ Margine inferno defiticnlato. 

 With the internal margin finely notched. 



Crassina. testa cordato-orbiculari subcompres^d, costis trdin's- -■ .wmh. 



versis paraltelis rotundalis, umbonibns prominentibus. "' 



Shell round heart-sliaped, rather flat, with transverse parallel 



rounded ribs, and the beaks prominent. 



s 2 



