Bill: There are a number of under the stones themes. As my bent seventeen and bent five examples show, the exact shape of the captured stones is not necessarily the key point. So a shape list can be neither comprehensive nor finite (if we can play on any size go board).
But I think that the question of under the stones conditions is worth a page or two. 209.2.144.1 has made a start. I think we can go further. :-)