Spotting

Welcome to Project Noah, Phil.field
Nice finding,i think you should began to compared this one with photos of Agaricus arvensis ,Agaricus campestris,Agaricus silvicatus and other Agaricus,is one of them for sure,my hint is on the first one Agaricus arvensis,but check your self furder,is allways good with fungi the phto id's are allways very tricky,congrats and thanks for sharing.
I hope you like the site as much we do; there are many features you can explore:
I invite you to go to http://www.projectnoah.org/faq where you will find the purpose and “rules” of Project Noah.
There is a blog http://blog.projectnoah.org/ where we post articles from spotters with special insight into different organisms.
There are also the chats for help with identification, and to comment on your own and others’ spottings.
Look at the global and local missions to put your spottings into: http://www.projectnoah.org/missions
Enjoy yourself here, see you around!