British distribution: Widespread but uncommon.
O. equina is a keratinophilic species that is sometimes found on old cast horns and on rotting hooves, as here on this manky old sheep's skull. The fruiting body consists of a more or less globose fertile head on a cylindrical stalk and can be regarded as a cleistothecium. The asci develop internally amongst a weft of hyphae rather than in an organised hymenium. The head then breaks open to release the ascospores.
While it is not known to pose any definite threat, its use of keratin may mean that it could plausibly infect fingernails. It is sensible to handle this fungus with caution.
One other Onygena species occurs in Britain: O. corvina, a smaller species on old feathers, owl pellets and similar material.