Three Jurassic Brittle Stars (Palaeocoma) - Lyme Regis
The black "staining" on the rock near the center of one of the brittle stars is pyrite. Often times these brittlestars have stable pyrite over the top of them, particularly on the central disk which spreads into the surrounding rock. This has to be ground away during preparation of the fossil. The grey spots on the rock near the central disk is remaining pyrite formations underneath the brittle star.