Large imprints found

[Large shell fossil]

Hello!

While living in Hawaii,  I found these, I really do not know much about them, they are heavy and solid, any ideas on what they are?  They were found on beach in sand like this, round and separate from a large rock, one is double sided 

[Fossildude19]

Tops of gastropod shells. Modern. 

[hemipristis]

they are the apex from modern cone snails. Locally, they're called 'puka shells'.  Holes are drilled in the center of the smaller ones and they are threaded together into puka shell necklaces

[Large shell fossil]

Thank you so much!