This beautiful red-orange mushroom is Amanita Muscaria, which has an extensive entry in Wikipedia. It’s common name is fly agaric, which isn’t particularly easy to remember either. (It was thought to kill flies when sprinkled in milk.) The genus Amanita includes most of the poisonous mushrooms, and Amanita Muscaria is not edible.
I have four lovely specimens growing underneath a pine tree. I recall seeing only one last year in the same place. The largest of these mushrooms is about ten inches in diameter and the top flattens out.
Here’s a young one, which you can see, is stout and round.
Dale Dougherty 