South African mystery...

So, here is a mystery for my readers: I have a couple of these little discs (around 3,5 cm in diameter) that I found during my travels in South Africa. If memory serves correctly I actually found them between the gravel in a car park near Gansbaai. Does anyone know what they are? They each have an imprint of a shell (Ammonite?) on one side and little protruding coral-like grow patterns on the other. Is it a fossil at all or… coming from the inside of a Kinder Surprise 🙂 My internet searches yielded nothing at all, so I would be very grateful to anyone knowing more about these little gems. Many thanks in advance!

Update February 1, 2016: thanks to reader Graham I now know these are not fossils at all, but the operculum (lid) of South African turbans or alikreukels (Turbo sarmaticus) Many thanks Graham for solving this mystery!