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. 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. d, 
shews 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 
FII. 3. p.) ’ 
I'igs. 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. 
Plate 53. V. 1. p. 434, Note, et seq. 
Fig. 1. 2. Upper parts of two nearly entire specimens of 
Briarean Pentacnnite, projecting in high relief 
from the surface of a slab, nearly two inches thick. 
