>I have a piece of a Japanese game sort of like "Concentration". Bivalve
>shells have illustrations inside, the matching valves with matching
>pictures. You turn them over and try to match them. The shell is a venerid,
>probably a Macrocallista or such...

The game is called 'Kai-awase' or 'match the shell'; it dates from at least
the 10th century, and the shells are usually Mactra chinensis. Antique sets
in their distinctive drum-on-legs carrying containers are fine things to
examine.