Can you tell me the official name for this fossil and how old it is please. - I found it on Littlehampton beach 46 years ago, on a day to the seaside. I think they used to import a lot of rocks and gravel to help against erosion, so it may have come from somewhere else in the UK.
I think it is a species of Spondylus (lower Jurassic to upper Tertiary (0-190m years old).
To quote from http://fossilidentification.weebly.com/bivalves.html:
"Spondylus are recognised by their unique Spines that give an extending effect to the ridges.
4 cm is a decent size for a Spondylus.
It has Spines around it's mouth; Growth lines are microsopic and are present but barely visible. It has equally spaced ridges; the pattern is basically large and small ridges alternating.
It has a symmetrical shell."
We see several of those characters in your specimen.
Go here and search for 'Spondylus',
and you'll see another example of a Spondylus from Littlehampton
(along with lots of other flint fossils)
Alex & Singha,
You're very welcome, and thank you.
There's still time to 'get involved'. The fossils (and minerals) are still out there, and they don't change much (though our names for them might).