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inferior termination of the lily encrinite. An effused lymph, or a 

 membranous expansion, appears to have involved this column, in 

 the same manner as was observed in that fossil, as well as in the infe- 

 rior termination of the turban encrinus ; and appears, in the same 

 manner, to have diminished the mobility of its articulations. 



The longitudinal section of a somewhat similar specimen, Plate XVI. 

 Fig. 12, shows more plainly the nature and use of this investing part. 

 The vertebral column is there seen surrounded with different layers of 

 *this substance, each of which appears to have been formed on the sur- 

 face of the column, and to have separated, and extended itself by its 

 growth to a considerable distance, at its inferior part, from the column 

 on which it had been formed, whilst it has still closely adhered to the 

 column at its superior part. 



A curious fact is here observable: in these membranes, which 

 at different distances surround the vertebral column, crenulated 

 articulations, similar to and exactly concurring with those of the 

 vertebrae, are plainly to be seen. By this curious conformation of 

 the organ of attachment, it is obvious that a more widely extended 

 base was obtained ; and in consequence of the points of union being 

 thus increased by so many concentric lines of adhesion, the firmness 

 of the adherence of the animal must have been well secured. From 

 the crenulated articulations which these tunics possessed in com- 

 mon with the vertebral column which they inclose, it is evident that 

 they must have possessed a certain portion of mobility, such, most 

 probably, as would be necessary for the animal to employ at this part ; 

 whilst, by the coherence of these tunics with each other, and with 

 the column itself in the superior part of the pedicle, the vertebral co- 

 lumn must here have acquired a considerable portion of strength. 

 The transverse section of another of these specimens, Plate XVI. 

 Fig. 14, serves to furnish us with a still more correct idea of the mode, 

 in which the osseous tunics or membranes were disposed, on the spot 

 to which the animal was affixed. 



