It's a bigun'!

This was dead on rocks about the mid tide line. Probably been out of the water for 4-5 hrs. By my estimations it measured approx 90cm diameter as it lies. No idea what it would be like if it was submerged. I found another a little way around the bay that was a a bit smaller. If I spotted 2 quite large specimens whilst walking the pooch and not looking for them there must have been more of comparable size.