Fossil Crinoidea.--The fossil crinoids, like the recent prototype above described, consist of an articulated column, and a receptacle formed of calcareous plates, and articulated arms or tentacula. They constitute two groups; the _Encrinites_, in which the ossicula of the column are subcylindrical and smooth; and the _Pentacrinites_, with a stem composed of pentangular ossicles, as in the living Pentacrinus. The petrified remains consist of the ossicula of the column, arms, and tentacula; of the plates of the receptacle; and of the peduncle, or process of attachment by which the animal was fixed to the rock. The peduncle is in some species flat and expanded, like that of the _Gorgonia_; in others, it consists of long jointed processes. These several parts are commonly found detached, and intermingled with detritus in the strata; throughout extensive beds of encrinital marble, vestiges of the receptacle are but seldom discoverable. In some localities the skeletons are preserved entire, and lie expanded on the surface of the layers of shale, clay, or limestone, as if the animals had been enveloped by the soft deposit when alive in their native seas. These remarks will serve to convey a general idea of the nature of the crinoidal remains which are scattered through certain rocks in such inconceivable quantities; for, much as the columns may differ in form, the ossicula in their markings, and the plates of the receptacle in their configuration and ornament, the same general type of structure prevails throughout the family. [Illustration: Lign. 90. Stems of Encrinites and Pentacrinites. Fig. 1.--Screw or Pulley-stone. _Derbyshire._ 2, 4.--Articulating surfaces of Encrinital ossicula. 3, 5.--_Entrochites_, or portions of stems of Encrinites. 6, 8, 10.--Portions of Pentacrinital stems. 7, 9.--Articulating surfaces of ossicula of Pentacrinites. ] Fossil Stems and Ossicula of Crinoidea.--(_Bd._ pl. xlix-lii. _Pict. Atlas_, pl. xlvii.)--The detached ossicula and stems are so common in many places, that they attracted the notice of the earlier collectors, by whom the single pieces were termed _trochites_ (wheel-stones), and the united series _entrochites_. In the north of England these fossils are called _Fairy-stones_, and the circular perforated ossicula _Saint Cuthbert's beads_; the latter were worn as ornaments by the ancient Britons, and are occasionally found in tumuli.