768 
Proceedings of the Royal Society 
kind of grappling root. The lower surface of the terminal joint 
is in all smoothed and rounded, evidently by absorption, showing 
that the animal has long been free. This character I have 
already noted as occurring in some specimens of P. mulleri and 
in one at least of P. asteria. I have no doubt whatever that it is 
constant in the present species, and that the animal lives loosely 
rooted in the soft mud, and may change its place at pleasure 
by swimming with its pinnated arms : that it is, in fact, interme¬ 
diate in this respect between the free species of Antedon and 
the permanently rooted fossil crinoids. 
A young specimen of P. wyville-tliomsoni gives the mode in 
which this freedom is acquired. The total length of this specimen 
is 95 mm., of which the head occupies 35 mm. The stem is 
broken off in the middle of the eighth internode from the head. 
The lowest complete internode consists of 14 joints, the next 
of 18, the next of 20, and the next of 26 joints. There are 
8 joints in the cirri of the lowest whorl, 10 in those of the 
second; 12 in those of the third, and 14 in those of the fourth. 
This is the reverse of the condition in adult specimens, in all 
of which the numbers of joints in the internodes, and of joints 
in the cirri, decrease regularly from below upwards. The broken 
internode in the young example and the three internodes above 
it are atrophied and undeveloped; and suddenly at the third node 
from the head the stem increases in thickness and looks as if 
it were fully nourished. There can he no doubt that in early life 
the Crinoid is attached, and that it becomes disengaged by the 
withering of the lower part of the stem. 
The structure of the cup is the same as in P. asteria and P. 
mulleri. The basals appear in the form of shield-like projections 
crowning the salient angles of the stem. Alternating with 
these w r e have well-developed first radials forming a closed ring 
and articulating to free second radials by muscular joints. The 
second radials are united by a syzygy to the radial axillaries, 
which as usual give off each two first brachials from their bevelled 
sides. A second brachial is united by syzygy to the first, and 
normally this second brachial is an axillary, and gives off two 
simple arms; sometimes, however, the radial axillary originates 
a simple arm only from one or both of its sides, thus reducing the 
