Can anybody please help with identification?

[lulu.shell]

Thank you Dave and Mikede for your suggestions. It doesn't appear to be Mercenaria, because it is much wider. But, Mikede, on your indication of veneridae family, I have done some searching on the interney, and come up with Tawera Gayi, also from Veneridae family, from Chile to S. Argentina. I think that the shape suggests this species.