- Diagram of a simple form of Crinoid, with five arms, each forking once; the one nearest the observer is removed to expose the tegmen of five orals.
- Monocyclica in which the dorsal cup is confined to the patina and occasional intercalated anals;: such ambulacrals or interambulacrals as enter the tegmen remain supra-tegminal and not rigidly united.
- Monocyclica with dorsal cup primitively confined to the patina and an occasional single anal; tegmen solid; portions of the proximal brachials and their ambulacrals tend to be rigidly incorporated in the theca.
Are either incorporated in, or pressed below, the tegmen by interambulacrals; all thecal plates united by suture, somewhat loose in the earliest forms, but speedily becoming close, and producing a rigid theca; mouth and tegminal food-grooves closed; arms pinnulate.
- Tegmen stout with conspicuous orals.
- Tegmen thin, flexible, with inconspicuous orals.
Tegmen flexible, with distinct ambulacrals and numerous small interambulacrals; mouth and food-grooves remain supra-tegminal and open.
Tt, The tegmen tympani.