I'd like to second the recommendation of the Audubon Field Guide. I think
it's best feature is that its photos are outstanding, even of micros.

However, not  only do you have to jump back and forth from photos to text
but the organization of the photos is supposedly according to their shape.
So many related species are widely separated in the photo section.

On a few days outing to the beach, I'd rather take that than any other
single book.

But how 'bout for when we get home? I've said it before: we really need
something more up-to-date and accessible than the 25 year-old out of print
2nd edition American Seashells.

David Kirsh
Durham, NC