a ee hc 
PENTACRINITES. 293 
PENTACRINITES.—The description of the recent Pentacrinus 
7 eaput-medusee (ante, p. 282), illustrates the characters of the 
crinoideans whose fossil remains are so familiar to the pale- 
_ ontologist, under the name of Pentacrinites. In these 
animals the pieces composing the receptacle are firmly arti- 
culated together ; the rays of the disk are fixed immediately 
to the summit of the column by special ossicula ; and the 
_ stem is composed of angular pieces, which are generally pen- 
_tagonal. The receptacle is small, and situated deep between 
the bases of the arms ; it is closed above by an integument 
covered by minute plates or flat ossicles (Lign. 94, jig. 2). 
The fossil remains of several species are abundant in the 
Lias and Oolite of Dorsetshire, Somersetshire, &c. Slabs of 
limestone may be extracted with the surface covered with 
these crinoideans, spread out as if floating in their native: 
element ; very commonly they are transmuted into sulphuret 
of iron, or have a coating of brilliant pyrites.* The neigh- 
_ bourhoods of Lyme Regis, and Charmouth, are celebrated for 
_ these organic remains. A small specimen of the arms of a 
pentacrinite on Lias shale is figured in Lign. 94, jig. 3. 
_ The arms in many of the plumose pentacrinites are very 
lone and thickly beset with side-arms, and minute pinne, 
all of which are composed of separate articulated ossicles, 
so that the number of bones in a single endo-skeleton of 
_ those crinoids amounts to from fifty to one hundred and fifty 
thousand distinct pieces. The Briarean Pentacrinite,t so 
named from its numerous tentacula, is literally a tuft of 
articulated processes, appearing like a delicate fibrous plume 
attached to a stem. The Pentacrinus Hiemere is a beautiful 
example of this type of crinoids, of which there is a noble 
group, comprising upwards of thirty individuals, on a slab 
* Pictorial Atlas, pl. li. lii. 
+ Pictorial Atlas, pl. xlvii. The Briarean Pentacrinite is fully illus- 
trated and described in detail in Dr. Buckland’s Bridgewater Essay, 
p- 484. 
