Need a better picture, minus the hand and maybe a ruler for size reference.
That is a Miller Meteor floor heat outlet or air intake, just don't remember exactly. Many people think that it is an ash tray. I have seen them in every ambulance and combination car that Miller Meteor built from the 1960's till the end of production.
One again, going from memory, they stay open and have a ball detent that holds it open. My car is in storage, but I may be able to have someone take a picture of it.