>On a recent trip I was able to do some shell collecting in New Jersey (Sandy Hook and Keyport beach). One of the finds was a 3 to 4 inch mussel with a brachidontes appearance. I collected several specimens, so it should not be uncommon, however, I do not seem to find in the general shell literature.  Has anybody from New Jersey and surrounding any idea which species this is?
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Our local large ribbed mussels are Geukensia demissa (Dillwyn, 1817), a common inhabitant of brackish water and marine marshes as well as more normal mussel habitat, and Ischadium recurvum (Rafinesque, 1820).  Geukensia is the only one typically reaching the size you describe.  Its beaks are non-terminal, so the shape is modioliform though the molecular data place it close to Mytilus, Septifer, Brachidontes, etc. and away from Modiolus.  Ischadium has terminal beaks and a more hooked shape, like Brachidontes.

    Dr. David Campbell
    "Old Seashells"
    Biology Department
    Saint Mary's College of Maryland
    18952 E. Fisher Road
    St. Mary's City, MD  20686-3001 USA
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"Mollusks murmured 'Morning!'.  And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!