Thanks for the reply.
It's just the top looks to be somthing wrong . Inside the red area its all seems to be 'hollow' you can lightly push and it's only the top layer left. Is this anything to worry about?
While I was giving my tortise a bath I noticed that on the side some of his shell was starting to 'chip' away. A closer look has shown me that the top 'dome' on his shell seems to have a small hole and the surrounding areas are also missing. You can lightly push and see its just the top layer...