Entoloma serrulatum

Scientific name: Entoloma serrulatum (Fr.) Hesler
Derivation of name:  Serrul- means "finely serrate" in
reference to the gill edges.
Synonyms:  Leptonia serrulata (Fr.) P. Kumm.
Common name(s):  Saw-gilled Leptonia; Blue-toothed
Entoloma.
Phylum:   Basidiomycota
Order:   Agaricales
Family:   Entolomataceae
Occurrence on wood substrate:  Saprobic; solitary or
several on the ground or on decaying, moss-covered logs and
stumps; June through September.  
Dimensions:  Caps 1-4 cm wide; stipes 3-8 cm long and
1.5-3 mm thick.   
Cap: Bluish-black fading to pale violet-gray with age.       
Gills: Subdecurrent to decurrent; whitish at first, then bluish-
gray to pinkish at maturity; gill edges toothed and dark
blue-black in color.
Spore print: Salmon-pink.
Stipe: Bluish-black, fading with age; white mycelium present
at base.
Veil: Absent.
Edibility: Not edible.
Comments: Altogether, this mushroom has a striking and
unique combination of characteristics.

More information at MushroomExpert.com:  

Figure 1. Young specimens. Photo © John Plischke III.

Figure 2. Older specimens with much of the color
faded away. Photo © Pam Kaminki.

Figure 3. Note the finely serrated and dark gill edges.
Photo © Gary Emberger.