PLATE 2, 3, 4. 
6. Small tubular bodies, united by transverse plates, 
forming the central part of the Entrochite. These probably 
served as a kind of ligament, in the recent animal, by 
which the joints were connected. They are found thus 
divested, in cavities occasioned by the removal of the exte- 
rior parts of the stipe. Specimens are not unfrequent in 
which this removal has but partially taken place. In these 
the tubes are generally chert, the outer parts of the Entro- 
chite spar, and the matrix to the whole chert. 
5. Less perfect specimens of these tubular bodies in 
brown chert. 
7. Specimen of the common Derbyshire grey marble; 
the figures in whieh are produced by various sections of the 
Entrochite. 
8. Perpendicular section of an Entrochite, in order to 
shew the internal structure and disposition of the parts 
above described, a. a. a. point out the different commissures; 
b. b. the ligament, which runs through the centre of the 
stem ; c. c. c. the transverse plates, by which the cylindric 
tubes, forming the ligament, are connected. The white 
parts of the figure show the internal pully-shaped structure 
of the joints; the black, the outer coat, or that part which 
fills up the groove of each joint, and constitutes the ambit. 
