Green agarics are not common, so Dermocybe austroveneta can often be identified with little trouble.
Dermocybe austroveneta (pronounced Dermo-sigh-be austro-ven-ee-ta) is commonly known as Green skinhead.
The cap of a young Dermocybe austroveneta is yellowish-green to dark green in the centre, slightly greasy when dry, slightly slippery when wet, with an umbo (dome-like swelling in centre of cap) that flattens with age.
Dermocybe austroveneta (pronounced Dermo-sigh-be austro-ven-ee-ta) is commonly known as Green skinhead.
The cap of a young Dermocybe austroveneta is yellowish-green to dark green in the centre, slightly greasy when dry, slightly slippery when wet, with an umbo (dome-like swelling in centre of cap) that flattens with age.

A close-up of the young cap shows the cortina (cobwebby veil, or remains thereof) stained rusty-brown from spores.

The cap starts off convex, flattening with age. Gills of varying lengths start off pale yellow, darkening to rusty-brown with age. The central white stem can be up to 100mm tall, tapering slightly upwards. The cobwebby veil and fibrous stem stains rusty-brown from maturing spores.
Pale yellowish gills of a young specimen - note the rusty-brown staining on the fibrous stem
Pale yellowish gills of a young specimen - note the rusty-brown staining on the fibrous stem

Broad, flat cap of an aging specimen - note the flattened dark green central umbo. The shade of green is variable.

Dermocybe austroveneta grows singly or in groups on the ground amongst leaf litter in Eucalypt forests. According to FungiMap, Dermocybe austroveneta is found in the south east of NSW, Victoria, Tasmania, the south east of South Australia, and the south west of Western Australia.
My sightings of Dermocybe austroveneta
[This will be updated with new sightings]
[This will be updated with new sightings]
Hunter Region Botanic Gardens - Heatherbrae, NSW - Jun 2009, Jun 2011, Jun 2012 (09, 11 and 12 specimens all in the same position).
Barrington Tops National Park - Mount Royal, NSW - Jun 2005
Cassilis - Cassilis Rest Area, Hunter Valley, NSW, native woodland, Aug 2010
Cassilis - Cassilis Rest Area, Hunter Valley, NSW, native woodland, Aug 2010
Brown gills of a mature Dermocybe austroveneta

Notice the slight tapering upwards of the stem.