fairy ring

That was why I wanted to see an individual and that Chlorphyllum molybdites was my suspicion as well

Lots of mushrooms grow in fairy rings, these are not Marasmius oreades. They're hard to ID without a close up shot of one but I'd suggest Chlorophyllum molybdites based on the apparent shape.

Do you have a close up of one of the mushrooms? Ava's right, the grass inside IS greener! Awesome!

This is called a fairy circle. It's interesting that grass within the circle is greener than the grass outside. The mycorrhiza must be feeding the grass. http://en.wikipedia.org/wiki/Mycorrhiza