What are these shells - and piece of coral?

[Hanalei]

Bottom is really just a shell fragment, not much to go on.  Possibly a piece of a Zigzag Scalllop, Evola ziczac.

Thanks for all of your help!  That's far more than I would've been able to figure out. 

That fragment, though, actually seems to be just about the entire shell.  Based on the inside of it, it's almost a perfect circle - there's only one small-ish section missing.