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we shall find beneath the cluster formed by the latter, an abbreviated column 
from which they proceed. 
On dissection, we find that the Comatule have series of calcareous secre- 
tions or ossicula exactly similar in their general plan and arrangement to the 
‘Crinoidea, and especially to the genus Pentacrinus, intended like theirs to 
‘sustain muscular action. ' 
Pentaconat Puate. At the base of the subglobose body of the Comatula, 
exists a pentagonal unperforated plate, slightly convex externally, and concave 
on the inside. It is analogous in situation to the first columnar joint of the 
‘Crinoidea, but as it is not required to transmit the passage to the alimentary 
canal (no prolongation of the celumn existing in this animal) it is without 
central perforation. , 
The Pexvis. On the margin of the pentagonal plate, rests an annular 
plate, resembling the rim of a basin, and forming with the former a basin-like 
cavity. It appears to oceupy the place of the pelvis of the Pentacrinite, it is 
consequently necessary that it should increase in proportion with the contained 
viscera, without altering materially its basin-like form ; yet as it is not formed 
of separate plates, and cannot therefore increase laterally their margins, 
another mode has been adopted, as I shall explain in proceeding. At 
the upper edge this pelvis-like plate is pentagonal, having between each 
of the angles a horse-shoe-like impression for the insertion of the first costal 
joint. Externally numerous auxiliary side arms proceed from the pelvis-like 
plate, which when they are broken off or removed, show the exterior surface 
of the plate marked with concave impressions (the points of their insertion) 
each surrounded by a hexagonal rim more or less perfect, according as their 
situation is near the central or marginal circumference of the plate. 
Avuxitiary Sipe Arms. Across the middle of each of the concave im- 
pressions on the pelvis-like plate, is a transverse ridge slightly perforated in 
the centre on which the first joint of the auxiliary side arm is attached. These 
arms, the formation of their joints, and their hook-like termination, resemble 
_in every particular those of Pentacrinus caput meduse, only that they are 
much shorter, and formed of a less number of joints. * 
* 
GROWTH OF THE Pe.vis anp Auxiviary Sipe Arms. It is perhaps not 
) 
