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137 
of the delineations intended to illustrate his work, (which he obligingly lent 
me) to draw up the following description :— ۱ 
The Centrar Prare* of the Marsupite may be considered as occupying a 
similar situation to those plates which form the pelvis in the Crinoidea inarticu- 
lata, since the other plates which cover the body of the animal are attached to 
it in a regular series. But being single only, not perforated in the centre, and 
having no concave impression at its exterior surface, we discover at once a 
striking dissimilarity, which points out that there existed no passage through 
the plate to an alimentary canal beyond it, and that consequently no columnar 
joint could have been attached to it; an inference which is confirmed by 
observing that the lower surface of this plate exhibits no mark of adhesion for 
a column. It is of a pentagonal form, somewhat elevated in its middle, 
marked at the exterior surface with subcrenulated ridges, arranged like those 
of Cyathocrinites rugosus, as described page 90. . 
Five PENTAGONAL CosTAL Prares. adhere to the lateral edges of the 
central plate, and are marked externally like it. | 
In the superior angles formed by the costal plates, are admitted ñve 
- hexagonal INTERcosTALS，also marked like the latter ; these, however, have 
in addition to the former markings, four conspicuous ridges radiating from the 
centre to the twolateral edges(which servefor the more firm adhesion ofthe inter- 
costals to each other) and to the superior margins (where the pentagonal scapula: 
adhere) over which they extend to the horse-shoe-like impression at their 
summit. 
The radiating subcrenulated ridges on the plates, the folds just noticed, 
and the lateral adhesion of plate to plate by simple sutures, plainly indicate 
that a muscular integument extended over these calcareous plate-like cone 
cretions ; that this muscular integument was capable of contraction, and ከ88 
left the ridges and folds above described as marks of its action, and corre- 
sponding with the appearances before observed in the Crinoidea, especially in 
Actinocrinites and Cyathocrinites, 
* Tam now doubtful, however, whether it might not be preferable to consider this plate as. 
analogous to the upper columnar joint of the Crinoidea, the next series as the pelvis, &c. in 
the manner proposed in the end of this article; but the letters of reference employed in the plate 
rendered it necessary to retain the above description also. 
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