Rhizome tufted. Fronds 2- to 4-pinnatifid, outer sterile, inner fertile; veins forked, free. Sori terminal, nearly circular, at length continuous. Indusium continuous with the reflexed margin of the pinnules. This genus is limited to the following species, which is widely dispersed throughout the north temperate and arctic regions. The name is compounded of hidden, and writing, in allusion to the concealed sori.

1. C. crispa, syn. Allosorus crispus. Parsley Fern, Rock Brake. - A dwarf tufted Fern with Parsley-like barren fronds, about 8 inches high, tripinnate; pinnules bi-tri-pinnatifid; stipes short. This plant is found in mountainous districts in Britain, and extends to Asia and North America.