Pavement Mushroom

There's not enough information here to fully identify this species. The are hundreds of Agaricus species and correctly identifying them can be hard enough with a microscope. Anything beyond Agaricus is mostly guesswork.

I guessed it's A. Bitorquis because of the way it grows out of the ground, plus, the horse mushroom is a very big mushroom. You can determine if this is the Torque (or Pavement -) mushroom by the two collars it has on the stem. This would be a distinctive sign.

Please have a look at Agaricus bitorqios: http://en.wikipedia.org/wiki/Agaricus_bitorquis

Agaricus species.