42 CONTRIBUTIONS 



precisely the same. The seat of the hinge within the 

 cavity of the beaks forms quite a level plate. 



Observations. This is certainly a very curious and in- 

 teresting hinge, and when we shall be able to see the 

 whole of it in connexion with the other portion of the shell, 

 it may be found convenient to erect it into a new genus. 



M. Grayi. Plate 1. Fig. 10. 



Description. Shell ovately triangular, solid, nearly equi- 

 lateral, obtusely angular behind, obscurely stria te; beaks 

 rather pointed ; cardinal teeth angular ; lateral teeth nearly 

 equally produced, crossed by equidistant minute striae; ex- 

 cavation of the palleal impression small, obtusely anguar; 

 posterior and anterior cicatrices deeply impressed ; cavity of 

 the valve rather shallow, of the beaks deep and sudden. 



Diam. N .3, Length .5, Breadth .6, of an inch. 



Observations. This interesting little species resembles 

 in the transverse striae of the lateral teeth the M. arctata 

 (Conrad) and M. donacia (Lamarck), both of which are 

 furnished with striae on the anterior as well as on the pos- 

 terior lateral teeth. Lamarck seems not to have observed 

 this highly interesting character, as he has not mentioned 

 it. Mr Conrad only mentions their being on the " poste- 

 rior lateral tooth." The cavity of the beak has the ap- 

 pearance of a hole made in the solid part beneath the hinge, 

 and possibly may have had a muscular attachment there. 



I have had some doubt if these species should remain 

 with the genus Mactra, but for the present it is, perhaps, 



