Does anybody know what this is?

[BristleWormHater]

I found this in NC a few years ago. It’s some kind of clam, but what happened to it? The shell on the right is the closest thing I could find to it but the shell on the left has a more curved end. Is this a fossil or something else?

 

[exnisstech]

Looks like natural erosion of shells I've found on the beach. But I have very limited time collecting.

 

[BristleWormHater]

I have a few shells that have a lot of erosion, but this is the only one that has sand cemented in it like in the second picture, so I'm not sure.

 

[BristleWormHater]

Also, the thing weighs around 5-6 pounds