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 h. 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. 436, Note.) 

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

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

 stellated crenulations on the articulating facets of 

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

 cles on the exterior of each columnar joint, for the 

 attachment of cortical contractile fibres. 13. c/, 

 shews the articulating facets of the auxiliary side 

 arms. (Goldfuss.) 

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

 tacrinites scalaris. (Goldfuss. PL 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 diffe- 

 rently disposed, to modify the amount of motion re- 

 quired at their respective places in the column. The 

 tubercular surfaces between the rays or petals of the 

 star indicate the action of the intervertebral contrac- 

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



Plate 53. V. I. p. 434, Note, et seq. 

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

 of Briarean Pentacrinite, projecting in high reHef 

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



