Geastrum saccatum

Common Name: None.
Description: Fruit body a round, bulblike sac whose outer wall splits, unfolds, and bends back into 4-8 starlike rays.
Habitat: singly or in groups around decaying stumps or in leaf litter in hardwood forests or under juniper and conifers. Quite common. Found widely distributed in North America.
Edible: Not edible.

Source: Mushrooms of North America by Roger Phillips.