262 DESCRIPTION OF CHALK CORALS. 
irregular in extent ; intermediate furrows of variable breadth ; abdominal cavities 
circular, slightly raised ; margin formed of lateral union of fibres. 
The only specimen examined (fig. 35,) was affixed to a Micraster (Spatangus, 
Auct.) about 14 inch in length and breadth; and the zoophyte extended over 
fully a third of the surface. The coral agreed in colour and opacity with the 
Micraster, though no distinct signs of rhomboidal cleavage were detected; an 
Alecto, however, which was associated with it, had a duller aspect, and apparently 
a more solid texture ; nevertheless it would be as correct to consider the Echi- 
noderm an internal cast, as to assume that the fibrous band represented only the 
interior form of a perished body. 
The mode of growth was very irregular (fig. 37), and seemed to have been chiefly 
influenced by the form of the Micraster ; but the diverging branches of the axis 
always issued from the side of an abdominal cavity, except in the case of a 
bifurcation. In the only good example (fig. 36) which was noticed of such a sub- 
division, the fibres separated longitudinally into two fasciculi, and then ranged 
onwards for about half an inch, when the two bands terminated at a visceral 
hollow. The manner of forming terminal additions was not very well shown, as 
it was difficult to distinguish between an immature development and an abraded 
portion. The most satisfactory case (fig. 36) consisted of two rudimentary 
cavities with a faint connecting band, the whole exhibiting only traces of struc- 
ture ; but the plan conformed strictly to that of other Anthozoa and of Bryozoa, 
visceral receptacles and associated structures being commenced and more or less 
advanced, far in front of a perfected portion, where alone exists the digestive 
apparatus, which affords the animal and mineral materials. 
The visceral hollows in general projected markedly above the axis, the fibres of 
the latter bending upwards and constituting the boundary wall. They were nearly 
circular and of great uniformity of size, but the inner diameter was scarcely half 
a line; and the whole breadth was usually less than that of the adjacent portion 
of the axis (figs. 36, 37). The depth was sometimes very small even in mature 
examples, and it rarely exceeded the diameter. The sides were highly inclined ; 
the base was slightly concave or rugose; and the margin, formed by the lateral 
union of the fibres, exhibited in the best preserved cases a serrated outline. 
The lamellz equivalents were well shown, eight having been distinctly counted 
in many cases ; and occasionally a wedge-shaped projection or lamella was de- 
tected. The distance between the regularly formed cavities varied from nearly 
three lines to about one; but two cases were observed of an imperfect cavity 
