Devil's toenail

R found this on the farm. Apparently it's a 200,000 million year old fossil from the Jurassic period. It was an extinct form of oyster. I read that North Lincolnshire (although this is south)has many of them littered around, deposited following the ice age. I'm learning all the time!
Too hot out there today for me. Back playing up so having a lie down, good excuse anyway!