Bivalve or brachiopod?

[Pleuromya]

Hello, I found this really nice shell today. I've seen you can tell bivalves and brachiopods apart by symmetry, but I'm not sure with this one, I thought bivalve, but I'm not certain. Also if anybody could tell me the genus or species, I'd really appreciate it. Thanks.

[TqB]

It's a bivalve - there's just enough asymmetry to tell. It looks like a species of Harpax (formerly Plicatula which will show more images) but bivalves can be hard to ID without knowing the beds they're from.

[Pleuromya]

2 minutes ago, TqB said:

It's a bivalve - there's just enough asymmetry to tell. It looks like a species of Harpax (formerly Plicatula which will show more images) but bivalves can be hard to ID without knowing the beds they're from.

Thanks. I found it in south west Northamptonshire. 

[TqB]

It'll be Jurassic, but lower to upper depending on area and whether it's from a quarry or the surface.

[Pleuromya]

25 minutes ago, TqB said:

It'll be Jurassic, but lower to upper depending on area and whether it's from a quarry or the surface.

Ah thanks. It was a surface find.