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. 
MM. Grayi. Plate 1. Fig 10. 
Description. Shell ovately triangular, solid, nearly equi- 
lateral, obtusely angular behind, obscurely striate; beaks 
rather pointed ; cardinal teeth angular; lateral teeth nearly 
equally produced, crossed by equidistant minute strize; 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. .3, Length .5, Breadth .6, of an inch. 
Observations. ‘This interesting little species resembles 
in the transverse striz of the lateral teeth the MV. arctata 
(Conrad) and JW. donacia (Lamarck), both of which are 
furnished with strize 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 1s, perhaps, 
‘- e 
* 
