Taken primarily from Kozloff, 1987, 1996 p. 282 (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 with prominent radial ribs, especially in the anterior one-third; length about 2.5 times the height, burrowing in clay and firm mud (introduced from the Atlantic) | Petricola (Petricola) pholadiformis |
| 1b | Radial sculpture barely apparent, consisting of closely spaced fine lines (these may be completely worn away); length less than twice the height; nestling in crevices and in burrows originally made by rock-boring bivalves (the shell is generally misshapen, conforming to the limited space in which the animal is living) | Petricola (Rupellaria) carditoides |
Petricola (Rupellaria) carditoides