Being thoroughly skilled in making a box clasp will allow you to
make a box clasp of almost any shape. As long as you can make the
internal box (which can be fit into almost shaped "box") and a tongue
to fit into it, the sky is the limit. It just takes careful planning
Study Alan Revere's instructions in his Professional Goldsmithing.
Follow it to the umpth degree a couple of times and I guarantee that
you'll be able to make any box clasp you want. Just change the shape
of the outside frame.