CO^CEYLIA—DITHYRA. 33. 131 



Turton, Conch. Diet. p. 236. 

 Mus. nost. Western and Scotch coasts. 



Shell an inch long, and an inch and a quarter broad, white cov- 

 ered with a chesnut or olive skin, very slightly angular and pro- 

 duced at the anterior side, with numerous regular equidistant round- 

 ed 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 

 impression under them on the hinder side, and a glossy lanceolate 

 one on the anterior side, both of them smooth ; inside glossy 

 white or cream-color : hinge with two strong teeth in each valve. 



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

 young of the Crassina sulcata, before the crenulations of the mar- 

 gins show themselves : but we have both the species from the size 

 mentioned above to less than a quarter of an inch, and in all their 

 stages of growth can readily distinguish the present species, even 

 when the valves are shut close, by the flatness and sharpnes of the 

 margin, which in Crassina sulcata is alwaj^s obtuse. 



** Margine interno denticulato. 

 With the internal margin finely notched. 



Crassina testa cordato-orhiculari subcompressd, costis transversis 

 parallelis rotundatis, umhonibus prominentibus. ^■ 



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

 ed ribs, and the beaks j^rominent. 



Sulcata. 



