21 



ten rings. I apprehend that a portion of animal matter remains always be- 

 tweeii the newly-formed ringand the former, perhaps interlacing with the radiat- 

 ino- muscle where it divides. A proof of this appears to be, that when decom- 

 position affects specimens, and converts them into a sort of .tchre, the rings 

 will separate, which could not happen, did not animal matter remain interposed 

 from their original formation. 



The enlarged columnar joints (?L. iv. fig. 8 to 12} are considerably thicker 

 than the others, are concave below, and at their superior surface more or less 

 convex, with a depression in the centre. They become gradually thinner to- 

 wards the middle, and show more numerous and more delicate radiating strias, 

 their points of division and the elevated rings are very distinct; at the latter, 

 sometimes a series of minute tubercles occur, where probably the covering 

 periosteum adhered more firmly. In consequence of the concavity of the inferior 

 surface having a greater curvature than the convexity of the superior surface, 

 each joint is thinnest towards the centre, and hence a hollow lenticular space 

 of a concavo-convex figure is formed between the two contiguous joints, which 

 may be considered as an enlargement of the alimentary canal. The joints 

 adhere by the last-formed rings, which probably afford a firmer connexion 

 from their being less calcareous, and are kept together more firmly by the thin 

 exterior muscle interlacing with the radiating ones. Their circumference is 

 somewhat less below, and contracts a little at the superior and lower surfaces. 

 Near the point of junction of the enlarged and unenlarged portion of the 

 column, an alternation of thicker with thinner joints, may very generally be 

 observed (T. i. fig. 2). This is common to all the Crinoidea, and has been ex- 

 plained as a provision of nature, to allow a greater power of motion to the 

 portion of the column where it approaches to the parts destined to procure the 

 animal's food. But I am convinced that this was also the place where new 

 joints are continually formed, at least as long as the energy of life permitted, 

 thus increasing the length of the column, as will be proved when describing 

 PENTACRINUS CAPUT MEDUSAE. 



The column at its lower extremity is more or less surrounded by calca- 

 reous matter of laminar construction, thereby adhering to extraneous sub- 

 stances ; this has been called by Mr. PARKINSON the PEDICLE or BASE. (PL. n. 

 fig. 1. to 10). I nave been fortunate enough to acquire a series of specimens 



