This is a species of Mycena. Coprinellus disseminatus has a similar shape and also grows in dense groups, sometimes a hundred or more within say a square metre. However, the Coprinellus has a dull to dirty white cap, typically with darker striations. In Mycena the gills stay white whereas in the species of Coprinellus the gills appear to turn black in mature specimens. What's happening is that the spores, initially pale become black at maturity and the colour of the mass of spores swamps the colour of the cells that make up the gill tissue. The flesh in the cap is so thin that much of the black colour shows through the cap tissue, giving that dirty-white colour and those dark striations.