The members of this order, Nidulariales, or bird's-nest fungi, are curious fungi of small size. They resemble, when mature, tiny birds' nests containing eggs, as the pouch in which the spores are developed opens at the top to form a nest or bowl or trumpet, and the globular cases in which the spores are contained have strong walls, and remain in the open pouch like eggs in a nest.
One genus of the order, Sphaerobolus, has two walls or layers to its nest and but one spore case or "egg." This "egg" is jelly-like, and is forcibly thrown from the nest when the spores in it are mature. While a part of this action is due to the mechanical working of the teeth, it is thought that underneath the spore case gases are formed which expand, and so help force out the "egg."
The other genera have but one wall to their nests. The genus Nidularia has ragged edges, the genus Cyathus is trumpetshaped, and the genus Crucibulum is bowl-shaped.