Taken primarily from Kozloff, 1987, 1996 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 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 |