Key:  Family Ostreidae:  Oysters

Taken primarily from  Kozloff, 1987, 1996  p 272 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	Valves generally much roughened and conspicuously frilly; height up to about 25 cm (introduced, but now widespread)	Crassostrea gigas
1b	Valves not much roughened and rarely showing any frills (the sculpturing is usually limited to irregular concentric lines); height not exceeding 15 cm	2
2a	Height up to nearly 15 cm (but generally much less than this); scar of adductor muscle deep blue-black (introduced in a few localities)	Crassostrea virginica
2b	Height up to about 5 cm; scar of adductor muscle not much darker than the rest of the interior of the valve	Ostrea (Ostrea) lurida

  Crassostrea gigas
  Ostrea (Ostrea) lurida