CONCHYLIA— />ir/IF/?^. 45. 203 



Shell fixed, inequiv^alve, irregular; with the beaks more or less 

 separated from each other and becoming unequal by age. 

 Hinge without teeth, with a cavity which is partly external and 

 in the lower valve becomes gradually elongated. Ligament 

 internal. 



This well-known tribe is always parasitical, being fixed to 

 rocks and other marine substances by their under valve. The 

 individuals or species are subject to much irregularity of figure, 

 and are generally coarse and rough. The hinge of the under 

 valve becomes much elongated by age, when the points of the 

 beaks recede from each other, and leave a gap between them. 

 Most of them have some minute granular denticulations on each 

 side about the hinge. 



OsTREA testa suborbiculari foliaceo- squamosa trigono-plicatd, Crista Gain. 



7nartjine interno vremilato. 

 Shell somewhat orbicular with scaly foliations and triangular 



plaits, and the inner margin crenulate. 

 Mytilus Christa Galli. Linn. Syst. Nat. p. 1155. 



Gmelin, Syst. p. 3350. 



Tttrton, Linn. Syst. iv. p. 289. 



Pennant, Brit. Zool. iv. p. 235. 



Montagti, Test. Brit, p, 166. 



Linn. Trans, viii. p. 104. 



'J'nrton, British Fauna, p. 164. 



Dillwyn, Descript. Catal. p. 299. 



Tttrton, Conch. Diet. p. 109. 



Chemnitz, viii. p. 52, tab. 75, fig. 683, 684. 

 2d 2 



