John said:
These are white gilled,no pink, then grey, then chocolate brown.
Chocolate brown spore print. Don't seem to stain quickly when bruised, rubbed or cut.
Stem easily removed from cap. Together in the field like a fairy ring.
Thin tall stalk-caps 2- 5" wide. Ring, Partial veil, No volva noticed

Todd said: but the texture of the cap surface looks very familiar,

Sava said:
John, this is no horse, no Agaricus.
The cap surface in every Agaricus is fibrillose
and would never crack in all directions, the way your picture shows.

What you have is Agrocybe praecox (or a closely related species).
These Agrocybe are very common spring mushrooms here, growing mostly on wood chips.
Note the farinaceous odor when you break the cap and squash it if needed to make the odor stronger.

Sava said: Lots of Agrocybe around. P
eople brought loads of them to the tables on Saturday blitz at Kelley Point.
Apparently, they are not all the same "A. praecox".
Joe Cohen got identified one of his posts recently asAgrocybe putaminum.
Tonight I came accross a nice paper by Else Vellinga on it and other wood chip mushrooms:
It's interesting that there are several species that get to new areas
with wood chips coming from who knows where.
Leratiomyces percevalii, also found by Joe Cohen recently, is one of them.
Leratiomyces ceres (= Stropharia aurantiaca) is another.
Neither of them seems to have become very common in our area yet.
(You'll find them in Else's article too.)

Mike said :
Let me add to what Sava said.
(His comment on the cap is a key one --
I have seen quite a few A. praecoxwith that type of cracking, which seems typical.)

Here are some characters that help me distinguish betweenAgaricus and Agrocybe.
a) The ring of your specimens, though well developed for Agocybe,
looks small and thin for an Agaricus.
Look at some photos of A. arvensis and similar species and see if you agree.

b) The stem of your specimens seems relatively slim and tall for an Agaricus,
especially for A. arvensis.

c) Smell. Pinch off a little flesh from a fresh specimen, crush, and inhale.
Edible Agaricus species usually have a distinctive anise smell;
bad ones, a phenolic smell, like a burning computer power supply.
Agrocybe has a quite different smell (as Sava pointed out).
Sometimes you can get a little of the anise smell by crushing a crimini or other store-bought Agaricus.
If so, it will get your nose oriented to the odor.

d) Dick Bishop recently pointed out to me that Agrocybe
often have a smooth feeling to the cap, like kid gloves.
I find that Agaricus usually feels more damp (though neither is slimy).
None of those things is 100% guaranteed,
but evaluating a bunch of characteristics together does help a lot,
especially after you know the species involved.
Good hunting!