137 



of the delineations intended to illustrate his work, ("which he obligingly lent 

 me) to draw up the following description : 



The CENTRAL PLATE* of the Marsupite may be considered as occupying a 

 similar situation to those plates which form the pelvis in theCrinoidea 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 PLATES 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 five 

 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 two lateral edges(whicl) servefor the more firm adhesion of the inter- 

 costals to each other) and to the superior margins (where the pentagonal scapulae 

 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 con- 

 cretions ; that this muscular integument was capable of contraction, and has 

 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. 



I am 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. 



T 



