126 



shells of this genus are less prominent, and differently 

 constructed from those of the G. Spondylus, the im- 

 possibility of the animal having the power to remove 

 the upper valve as the shell increases in size, is equally 

 manifest. See Sovverby's judicious observations on this 

 genus, No. 6, of his Genera of Shells. 



Margin of the valves plain or waved, but not plaited 



Ostrea edulis 



Ostrea ruscuriaua 



hippopus 



Virginica 



borealis 



Canadensis 



Adriatica 



excavata 



cochlear 



mytiloides 



cristata 



sinuata 



gallina 



trapezina 



numisma 



tuberculata 



lingua 



rufa 



tulipa 



margaritacea 



Brasiliana 



gibbosa 



scabra 



austral is 



rostralis 



elliptica 



• parasitica 



haliotidaea 



denticulata 



deformis 



• • • spathulata 



• fucorum 





