63 ፣ 
dual deposition of calcareous matter in these places. It forms at this period 
(fig. 1.) a transverse round ridge, over which the muscular part is drawn in 
acutely. Ina more advanced stage of growth (fig. 4.) the petals increase so 
much as nearly to efface the intervening space, and hence the crenated line of 
adhesion between these joints, arising from the insertion into each other of the 
radii and notches surrounding the petals, may be traced continuously round 
the cireumference, uninterrupted as in younger specimens by intervals where 
the margin issmooth. The whole joint being at this period calcareous (having 
only a muscular integument) the column has a smooth pentagonal appearance, 
with a slight elevation near the junction of every two joints, leaving, however, 
a trifling ridge between for the action of the small portion of muscle extending 
to the exterior circumference, over and between the radii of the petal-like for- 
mations. The ridge mentioned before has now disappeared, and in its stead we 
trace a slightly elevated line (fig. 3.) waved conformably to the power exercised 
on it by contraction of the muscles between the joints. A further contraction 
(fig. 5.) breaks this line into three or four minute tubercles, and sometimes _ 
by lateral contraction produces two other tubercles, one above and one below 
the line. 
t 
I understand, that at Lyme, columns of from four to five feet long occur, 
belonging to this species. 





















