Panaeolus

Found on side of trail in Mt Park 12/19/14
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Judy said:

Yes, you do have a species of Panaeolus, but without microscopic examination, it would be hard to tell which one. Between species, the spores can vary quite a bit in their reaction to concentrated sulphuric acid.

The white on the gill edges are cheilocystidia, the sterile spacing cells between basidia, or maybe even not having basidia among them. The size and shape of them is also a separating feature between species.

The mottled gill sides is because the spores vary in their rate of maturity - not all maturing at the same time, as in some other genera.

Psathyrella is quite similar, but growing with well rotted wood (often nearly gone from the soil, but still there), and Panaeolus generally is on dung, or highly nitrogenous soil (where animals pee a lot) in either soil or grasses.

The gills were probably attached to the stem, because that end of the gills are so uniformly blunt. You can also tell by looking closely at that area at the stipe top after the cap is pulled off because you can see little ridges or lines where the gills were.

This feature can vary, however, and some species have almost free gills. This feature is more ambiguous in Panaeolus than Psathyrella. Your species is probably closely related to the group that includes Panaeolus foenesecii.