I suspected there was a fossil hiding in this concretion based on what I thought was a leg or claw visible on the side of the concretion. It was such a soft matrix that I could use a combination of a small screwdriver and a wooden toothpick to remove the siltstone to expose the crab. It took about 5 hours to complete as I had to stop and add a consolidant (B72 paraloid) to strengthen the fossil and stop if from flaking and getting damaged.

After hours of careful work, a fossil crab was revealed. I suspect it is a moult, the carapace was shed when the crab outgrew it, as there are no legs and it appears to be hollow.

This could be my oldest crab fossil, it's in the region of 19-million-years-old.