03 



dual deposition of calcareous matter in these places. It forms at this period 

 (fig. l.)a transverse round ridge, over which the muscular part is drawn in 

 acutely. In a 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 circumference, uninterrupted as in younger specimens by intervals where 

 the margin is smooth. 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. 



I understand, that at Lyme, columns of from four to five feet long occur, 

 belonging to this species. 



