86 EXPLANATION OF PLATE 52. 



Fig. 4, the joints are of three degrees of magnitude ; 

 those at a. being the largest, those at c. the smallest 

 and thinnest, and those at b. of an intermediate size. 

 The edges of c. appear at the surface only upon the 

 salient portion of the column, Fig. 4. (See V. I. p. 

 328, Note.) 



Figs. 6, 7, 8, 9, 12, 13. Portions of the vertebral column 

 of Pentacrinites basaltiformis. 6, 8, 12, show the 

 stellated crenulations on the articulating facets of 

 different parts of the column ; 7, 9, show the tuber- 

 cles on the exterior of each columnar joint, for the 

 attachment of cortical contractile fibres. 13. d, 

 shows the articulating facets of the auxiliary side 

 arms. (Goldfuss.) 



Fig. 10. Articulating facet of a columnar joint of Pen- 

 tacrinites scalaris. (Goldfuss. PI. LII. 3. h.) 



Fig. 11. Fragment of a column of the same species. 

 The joint d. bears sockets for the articulation of the 

 side arms. The other joints have large tubercles 

 for the attachment of cortical fibres. (Goldfuss, PI. 

 LII. 3. p.) 



Figs. 14, 15, 16, 17. Articulating surfaces of joints in 

 different parts of the column in Pentacrinites sub- 

 angularis. The mechanism of each star seems dif- 

 ferently disposed, to modify the amount of motion 

 required at their respective places in the column. 

 The tubercular surfaces between the rays or petals 

 of the star indicate the action of the intervertebral 

 contractile fibres. (Goldfuss, PI. LII. 1. m. n. o. p.) 



Plate 53. V. I. p. 327, Note, et seq. 



Fig. 1. 2. Upper parts of two nearly entire specimens 

 of Briarean Pentacrinite, projecting in high relief 

 from the surface of a slab, nearly two inches thick, 



