Is this white Coral?

[Unitedstatesofamerica1]

5 1/2 inches long
3 1/2 inches wide

 

[Back-of-the-boat]

That looks like a conch shell that only the inside whorl is left.

 

[maxpower]

yup broken conch

 

[yaxthri]

The lots of holes were made by a boring sponge maybe Cliona celata.
I'm guessing that you are not living near the sea or you would have identified a broken shell yourself...
Where do you hunt, where did you find it? Could be a fossil.