Agaricus xanthodermus (Genevier)  var. lepiotoides (Maire)

Some European authors have pointed out to this variation of A. xanthodermus defined by the distinctive Lepiota-like cracks and fissures that remind one of scales. . It is not universally accepted though. Some authors believe that the fissures and cracking of the cap are environmentally dependent. I have observed patches growing in the same lawn where some groups develop these features and some do not. The differences seem to persist despite the shared  environment.

The picture shows a mixed collection of Agaricus xanthodermus v. xanthodermus and v. lepiotoides -- growing side by side in the same lawn demonstrates that  the cracked cap is not environmentally induced, but the variations are rather distinct.

Macrolepiota rachodes (l) and Agaricus xanthodermus v. lepiotoides (r)