98 



ever is more nearly allied to the G. Chama, possessing, 

 like the species of that genus, two separate lateral mus- 

 cular impressions, with the faculty of affixing itself by 

 the lower valve, and in fact has only been separated 

 from it by not having any tooth at the hinge, and by 

 the substance of the shells, having a pearly appearance, 

 and being lamellar, as in the oyster. They are of consi- 

 derable size, and of an extremely irregular form, occa- 

 sioned by the lower valve adapting itself to the shape of 

 the body to which itisaffixed. The interiorof the valves 



is covered with very singular hollow globular, irre- 

 gularly formed concretions, beneath the pearly coating, 

 which may probably be only accidental. It has also 

 a subcylindrical callosity attached to the base of the 

 shell, which does not exist in the second species de- 

 scribed by Lamarck. Shell irregular, inequivalve, ad- 

 hering by the lower valve: apices short, and appear- 

 ing as°it were forced into the base of the valves. Hinge 

 without teeth, waved, subsinuous, unequal; two lateral 

 and oblong muscular impressions: ligament external, 

 winding, and partly penetrating the shell. 



Specimens of this very rare shell exist in the Pro- 

 vost of Eton's cabinet, and in that of the late Earl 

 Taukerville. 





