How to remove Quail Radiator Cap

[Steve_KS]

This is a dumb question but how do you remove the quail radiator cap from the car. It was on my car when I got it. I assumed a quarter turn then lift off like a normal radiator cap but it didn't come off easily and I don't want to scratch or bend something. My searches haven't turned up anything conclusive.

To open my quail I have to firmly grasp the bottom to keep it from turning then turn the bird on top 1/8 of a turn then it hinges open.

Thanks