Short-spined sea urchin

Thanks for your inputs!

It could be B. latercarinatus, it would fit the location if this was found washed up on a beach! I don't think this is fossilised as I just noticed the hole in the shell so B. oblongus is out.

This is indeed a kind of sea urchin... or at least it was! It's called a heart urchin, and will be hard to ID much further than that. My gut things it is something in the Brissus genus, have a look at some of these samples from the Natural History Museum in London: http://www.nhm.ac.uk/research-curation/r... I think in particular it might even be B. oblongus http://www.nhm.ac.uk/research-curation/r... But it's hard to tell from the skeleton, especially just on photo of it. If you can, post some more angles of this (like the bottom), or also go through the Natural History Museum's pages!