Hericium erinaceus

Scientific name:  Hericium erinaceus (Bull.) Pers.
Derivation of name:  Hericius means "hedgehog." Erinace-
pertains to the prickly European hedgehog, Erinaceus
europaeus.
Synonyms: Hydnum erinaceus Bull.  
Common name(s):  Satyr's beard; Lion's mane; Hedgehog
mushroom; Bearded tooth.
Phylum:   Basidiomycota
Order:   Russulales
Family:   Hericiaceae
Occurrence on wood substrate:  Saprobic and parasitic; often
solitary on living trunks of deciduous trees or on fallen logs;
August through November.  
Dimensions: Fruit body 10-25 cm wide and high; individual
spines 2-7 cm long.   
Description: A whitish (becoming yellowish in age) mass of
hanging spines resembing a beard. The fruit body and spines are
unbranched.      
Edibility: Edible when young, becoming sour with age.
Comments: Culitivated varieties of this mushroom are sold as
"Pom Poms."
  
More information at MushroomExpert.com:
More information at TomVolkFungi.net:

    

Figure 1. Hericium erinaceus. The spines are attached
to a short, tough, rooting base. Photo © William Roody.

Figure 2. Another view of bearded tooth. Photo © Larry
Grand.

Figure 3. The cut ends of logs and branches are a
common location for Hericium erinaceus.
Photo © Gary Emberger.