FOSSIL FAUNA. Ill 



PLATE XLVI. 



Pentacrinus. 



Fig. 1 . Specimen of a recent Pmtacrinus Caput Medusae, from the Carribean Sea. 



The Lily-shaped animals {Crinoidea), so named from a fancied resemblance of some species 

 when in a state of repose to a closed lily, may be compared to a Feather -star {Comatula) fixed to 

 a jointed column, with its mouth upwards ; the base of the stem being attached to the rock by 

 root-like processes. The only known living genus inhabits the seas of the West Indies, and the 

 specimen figured represents the body (or upper part of the animal), with a considerable portion 

 of the stem remaining attached. The Crinoidea are divided into two grouj^s ; Encrinites, having 

 the ossicula (little bones) of the stem rounded, and Pentacrinites, in which the ossicula of the 

 colunm are pentagonal, or angular. The Crinoidea are characterized by having a fixed base, 

 a column or stem composed of numerous separate articulated pieces of a solid calcareous sub- 

 stance, supporting on its summit a vase, or receptacle, formed by a series of closely adjusted 

 plates, which contain the body, or viscera. The upper part of the receptacle is covered by 

 a plated integument, on one side of which an aperture or mouth is placed. From the upper 

 margin proceed five articulated tentacida or arms, which subdivide into branches that in some 

 species are very numei-ous and of extreme tenuity. On the inside, the arms are beset with 

 articulated cirri or feelers. The joints composing the column are perforated by a central opening ; 

 there are also side-arms, that radiate from the column in groups of five at different points. 

 When the animal is alive, the skeleton is covered by a soft integument, as in the star-fishes, and 

 the arms spread out and expand, forming a net, by which living prey is captured and conveyed 

 to the mouth by the tentacula, in the same manner as in the fresh-water polype or Hydra. 



The fossil remains of Crinoidea consist of the ossicula of the column, arms, and tentacula ; 

 of the plates of the vase, or receptacle ; and of the peduncle, or base of attachment. This 

 family of Radiaria, though now of such excessive rarity, swai-med in the seas that deposited the 

 ancient secondary strata ; whole mountain chains and extensive ti-acts of country are composed 

 of strata almost entirely made up of their fossil remains.' The number and species of genera is 

 very great. 



Fig. 2, is a remarkably beautiful specimen of the receptacle of a Pentacrinite from Gloucester- 

 shire, showing the arms introverted, as if the animal had suddenly perished while 

 in the act of closing over its prey ; the stem is wanting. 

 Fig. 3. A spongite {Chenendopora subplana, of Michelin) from the greensand of the Vale of 

 Pewsey, in Wiltshire. 



^ Wonders of Geology, vol. li. p. 645. MedaU of Creation, p. 312. 



