Many thanks - but - after poking around the whole chrome rim with a broad knife
I was able to separate the tabs which fit into slots on the hood.
But the bugger won't come off! When I gently pry it away it snaps back quite firmly.
I'm afraid I'll break the glass.
Something else is retaining that thing on there, and I'm thinking it might be some kind of spring-loaded clip arrangement form the 50's.
Thanks for your kind help and the merriest of Christmases to you and all the folks on here who help others.
Jim in Dartmouth MA