Nora,

You might want to check out:

Marine Shells of the Pacific Northwest (1971) by Tom Rice and

The Intertidal Bivalves of British Columbia (1978) by D. B. Quayle
(published by the British Columbia Provincial Museum- handbook #17).

The former contains lots of color photographs of some of the smaller
bivalves, the latter has beautiful drawings that include good internal
details (muscle scars, hinges, pallial line).

These may not help with the more recently introduced species but I have
found them to be useful references for mollusks in BC and elsewhere in
the Pacific Northwest.

Good luck,

Phil Liff-Grieff
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La Crescenta, CA