Coprinus micaceus

Scientific name:  Coprinus micaceus (Bulliard:Fries) Fries
Derivation of name:  Micaceus means "glistening" and
describes the shiny particles on the cap.
Synonyms: Coprinellus micaceus (Bull.:Fr.) Redhead, Vigalys
& Montcalvo. This is actually the most recent name for
this mushroom, reflecting the division of the genus Coprinus
into four genera. The Miller field guide (2006) for example,
uses this name. 
Common name(s):  Mica cap.
Phylum:   Basidiomycota
Order:   Agaricales
Family:   Coprinaceae
Occurrence on wood substrate:  Saprobic; densely clustered
around stumps, wood debris, at the base of standing dead or
dying trees or in grassy areas from buried wood; April through
October.  
Dimensions:  Caps 2-5 cm wide; stipes 2.5-8 cm tall and 2-5
mm thick.   
Cap:  Reddish-brown to tawny, becoming grayish; surface
covered by glistening granules that are soon lost; cap radially
lined almost to the center.        
Gills: Attached to nearly free; white, becoming black and inky
with age but not entirely dissolving. 
Spore print: Black.
Stipe: White
Veil: Absent.
Edibility: Edible.
Comments: There are several other species of Coprinus which
grow on wood, are not included in my keys, but differ
from Coprinus micaceus. For example, C. disseminatus is
smaller and its gills do not become inky. Another is C. radians
but it has a mat of orange hyphae around the stalk base.

More information at MushroomExpert.com:  


Figure 1. A clump of mica cap. Photo © Pam Kaminski.

Figure 2. The caps are conspicuously striate. Photo ©
William Roody.

Figure 3. The gills of the mature specimens on the left are
partially auto-digested into an inky fluid. Photo © Larry
Grand.

Figure 4. The glistening mica-like particles are visible on
these young specimens. Photo © David Work.