Isle of Wight ID help please (2nd find)

[MrsD]

Hi again, I’ve just posted my first find, and here is another I would like help with please. Found on the Isle of Wight Jurassic coast, grey coloured rock around 8cm in length, with what looks like some fish bone type markings. On the reverse side of the same rock is a round light grey circle about 1cm across with a thin white circle surrounding it. Please can anyone help with more information... thanks!