Onygena equina

About

Onygena equina, commonly known as the horn stalkball, is a species of fungus in the family Onygenaceae. The fungus grows on putrefying hooves and horns, and can digest the keratin in those substrates. Fruit bodies are small and white, with thick stipes supporting a "head" shaped like a flattened sphere. The skin, or peridium, of the head appears powdery or like a white crust, and breaks open in maturity, falling off in irregular pieces to expose the pale reddish-brown powdery spores within. The fungus is known from Europe and North America.

Summary from Wikipedia