CHAP, TX.] THE DEEP-SEA FAUNA. 449 
from the symmetry and compactness of the Apio- 
crinidee of the Jurassic period. 
The anchylosed ring of first radials is succeeded by 
a tier of free second radials, which are united by a 
straight syzygial suture to the next series—the radial 
axillaries. The surface of the funnel-shaped dilatation 
of the stem, headed by the ring of first radials, is 
smooth and uniform, and the second radials and 
radial axillaries present a smooth, regularly-arched 
outer surface. The radial axillaries differ from the 
corresponding joints in most other known crinoids 
in contracting slightly above, presenting only one 
articulating facet, and giving origin to a single arm. 
The arms, which in the larger specimens are from 10 
to 12 mm. in length, consist of a series of from about 
twenty-eight to thirty-four joints, uniformly trans- 
versely arched externally, and deeply grooved within 
to receive the soft parts. Each alternate joint bears 
a pinnule, the pinnules alternating on either side of 
the axis of the arm, and the joint which does not 
bear a pinnule is united to the pinnule-bearing joint 
above it by a syzygy: thus joints with muscular 
connections and syzygies alternate throughout the 
whole length of the arm. 
The pinnules, twelve to fourteen in number, con- 
sist of a uniform series of minute joints, united by 
muscular connections. ‘The grooves of the arms and 
of the pinnules are bordered by a double series of 
delicate round fenestrated calcareous plates, which, 
when the animal is contracted and at rest, form a 
closely imbricated covering to the nerve, and the 
radial vessel with its delicate czecal tentacles. 'The 
mouth is placed in the centre of the disk, and radial 
GG 
