198 CO^GRYLIA—DITHYRA. 44. 



Dillwyn, Descript. Catal. p 310, 



Turton, Conch. Diet. p. 110. 

 Mytilus edulis. Var. Chemnitz, viii. p. 169, tab. 84, fig. 751. 

 Mus. nost. On the western coasts. 



A very elegant shell both in color and figure, seldom reaching 

 to two inches in length, covered when fresh with a dark olive skin, 

 under which it is blue with white rays ; and is distinguished from 

 the radiated variety of the common Mussel in its younger state, by 

 having only two or three tubercular teeth under the beaks. 



44. MOBIOL A— LAMARCK. 



Testa subtransversa, aequivalvis, latere postico brevissimo ; umbonibus 



subterminalibus, ad latus brevius. Cardo edentulus. Ligamentum 



marginale, exturnum. 

 Shell somewhat transverse, equivalve, with the hinder side very short ; 



the beaks nearly terminal, and placed at the shorter side. Hinge 



without teeth. Ligament marginal, external. 



This genus is separated from the Mytilus by sufficiently clear 

 characters ; the want of teeth in the hinge, and the lateral but 

 nearly terminal position of the beaks. The species are sometimes 



