Note smooth stem, white flesh, veil, note also color of gills. In contrast to Agaricus the gills are attached to the stalk.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/32769754@N00">apa3a</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/32769754@N00/563051237/">2007-06-15 6 Stropharia Rugosoannulata</a>