Calliostoma zizyphinum

... or Painted Top Shell to you and me. I found several on Baleshare beach today and the low sunlight brought out the colour in them. That colour is a real hint of the tropical and to my mind the Painted Top Shell is the prettiest of the various shells you find on the shore here - even if its name is a bit "as it says on the tin". It also helps that they are quite big and easy to see.
I love the shapes in this photo, two-dimensional and three-dimensional objects captured in the same image. Projective geometry in action.