Shells small to medium-sized, of extremely variable shapes, white to flesh-coloured, thin, and provided with a thick and spiky periostracum. Previously comprising only cap-shaped species, the family includes nowadays the group formerly known as Trichotropidae.
 

« Shell free, univalve, Phrygian cap-shaped; summit more or less acute and coiled; aperture entire, rounded; inside with two muscular immpressions. […] the circular lip of the cap-shells is not planar, but undulates in relation to the rocks or whatsoever bodies the mollusc to which it belongs is attached to. […] The two internal muscle scars are also rather noticeable: tear-drop shaped, they join, in truth, almost imperceptibly near the top; downwards they widen. » – P. D. de Montfort: Conchyliologie systématique et classification méthodique des coquilles vol.2, Paris 1810, p.54.