Shells, Skulls from Beach Last Night

Not sure about the big skull (which animal, that it). I'm going to bleach it in hydrogen peroxide. The seagull skull is a nice one, going to get it stripped down and bleach. I want to retain the yellow color of the beak. Most of the shells shown here are these thin translucent wafers. They have slight iridescence like abalone shell colors. I've strung them together to make windchimes. I don't know what they are, can't find them in our books on seashells.