I may have two possible species Agrocybe
praecox and Agrocybe
molesta. The latter one seems more
amongst the grass south of the Reservoir on the
upper slopes of
These are probably a species of Agrocybe.
Agrocybe are reported to disintegrate quite quickly. With these it seems they remain firm for a week, but when they suddenly become soapy they will fall to pieces within a day or two if wet. If dry they may dry out if the identifiations are correct.