88 EXPLANATION OF PLATE 53. / 



base of the side arms, with the larger joints of the 

 vertebral column. See V. I. p. 439. Note. (Original.) 



Fig. 8. Magnified Section of a portion of a Column in 

 the Oxford Museum. The joints, as in PL 52, Fig. 

 4, 5, and in PL 49, Figs. 3, 4, are alternately thicker 

 and thinner; with a third, and still thinner joint 

 interposed between them. See V. I. p. 435, Note. 

 (Original.) 



Fig. 8^ Nat. size of Fig. 8. 



Fig. 8". Portion of a Column, shewing the manner in 

 which the edges of the thinnest plates, c, are visible 

 along the salient angles only. In the intermediate 

 grooves the thicker plates, of the first and second 

 sizes, fl, bf overlap and conceal the edges of the 

 thinnest plates, c. The principle of this mechanism 

 is the same as in Pentacrinites subangularis, PL 

 52, Figs. 4, 5, and in Encrinites moniliformis, PL 

 49, Figs. 3, 4 ; but the circular form of the column 

 in the latter, causes the smallest plate, c, to be 

 visible around its entire circumference. See V. I. 

 p. 435, Note. (Original.) 



The bases of two side arms are seen in two of the 

 grooves, articulating with the uppermost large joint 

 of this column. On other large joints are seen the 

 sockets from which similar side arms have fallen. 



Figs. 9, 10, 11, 12, 13. Various stellated forms on the 

 articulating surfaces of Vertebrae, preserved in the 

 dislocated mass beneath Figs. 1, 2. These petal- 

 shaped, and crenated rays were probably adapted 

 to produce various degrees of flexibility, according 

 to their respective places in the column. The small 

 Vertebra on Fig. 13, is derived from another indi- 

 vidual. (Original.) 



The aperture at the centre of all these Vertebrae 

 was for the passage of the alimentary canal, which 



