436 ROOT OF PENTACRINITE. 
ally fixed to the bottom of the sea, or to some 
extraneous floatmg body, the flexibility of the 
jointed column, which forms the stem, was sub- 
servient to the double office, first, of varying, in 
every direction, the position of the body and arms 
in search of food, and secondly, of yielding, with 
facility, to the course of the current, or fury of 
the storm, swinging, like a vessel held by her 
cable, with equal ease in all directions around 
her moorings. 
The Root of the Briarean Pentacrinite was 
probably slight, and capable of being withdrawn 
from its attachment.* The absence of any large 
Figs. 11. and 13, the Vertebree (d.) present five lateral surfaces 
of articulation, whereby their side arms were attached to the ver- 
tebral column at distant intervals, as in the Pentacrinus Caput 
Medusae, PI. 52. Fig. 1. 
The double series of crenated surfaces, which pass from the 
centre to the points of each of the five radii of these star-shaped 
vertebrae, PI. 52. Figs. 6. to 17.; and PL 53. Figs. 9. to 13, 
present a beautiful variety of arrangements, not only in each 
species, but in different parts of the column of the same species, 
according to the degree of flexion which each individual part 
required. 
* Mr. Miller describes a recent specimen of Pentacrinus Caput 
Medusae, as having the joints next the base partially consoli- 
dated, and admitting but little motion, where little is required ; 
but higher up, the joints become thinner, and are disposed 
alternately, a smaller and thinner joint succeeding a larger and 
thicker, to allow a greater freedom of motion, till near the apex 
this change is so conspicuous, that the small ones resemble thin 
leather-like interpositions. He also observed traces of the action 
of contractile muscular fibres on the internal surfaces of each 
vertebra. 
