Timespanner in NZ has a description of an unusual toilet seat, another invention that did not catch on, but it reminded me of a toilet from my childhood and I can't remember where it was.
I think it was a pit toilet, rather than a septic or sewered model. As you sat on the seat, two spring activated stainless steel flaps opened below you. As you removed your weight from the seat, the flaps closed. I can only guess that the flaps were to stop the odour rising from the pit below and or keeping flies out of the pit. Don't worry fellas, the flaps were low enough to not accidentally snap shut on anything.
Anyone come across a model like this?