DESCRIPTION OF CHALK CORALS. 297 
their being regarded as different states of one zoophyte. The Alecto, however, 
preserved its essential character of a single series of tubes, and where it appeared 
to issue from one or opposite sides of the other coral, due attention showed an 
overlying ; and the Alecto in its onward course dichotomosed without any struc- 
tural enlargement ; whereas the Diastopora assumed a club- or fan-shaped increase 
prior to subdivision, and the new branches had two or more rows of apertures : 
moreover, on the Ananchytes where a similar association occurred, the tubes of 
the Alecto exceeded in size those of the Diastopora. 
The Micraster which afforded the most abundant display of this coral was 
about two inches in length and greatest breadth, and the zoophyte occupied 
about two-thirds of the upper surface. No direct centre of divergence was ob- 
served, the branches ranging in every possible direction ; and springing from 
detached points where germs or ovi had settled. In the more regular portions, 
the plan of ramification was strictly dichotomous (fig. 1 a) ; but many deviations 
due to local or mutual interference occurred ; and no uniformity existed either 
in the distance between the divergences, or in the alterations in the breadth of 
the branch precursory to bipartition. The narrowest, or what might be con- 
sidered first-formed portions, had two or three series of apertures, the breadth 
increasing more or less rapidly, but without any uniform plan; while from this 
augmented development the new branches issued by a true dichotomization, 
though not always into two equal portions of the previous number of tubes 
(consult the figures of MM. Michelin and Goldfuss). The range of the tubes 
was almost constantly visible, the surface being slightly convex ; but the amount 
exposed varied greatly. The apertures were uniformly inclined upwards, and to 
about an equal extent ; and no changes depending upon age, as a marked filling- 
up or thickening of the surrounding general surface, by which they would be 
depressed, were noticed. The plan of developing additional tubes was best 
shown in abraded branches (fig. 1 6), where interpolations as well as terminal de- 
velopments could be clearly detected. 
Tab. XVIIL. B. figs. 2 & 2a. 
The curious fossil represented by the above figures consists, so far as it is 
known, of long blade-like foliations, which are composed of two opposite layers 
of tubes ; and the exterior displays transversely diverging rows of apertures with 
an intermediate, minutely tubular lamina, extended marginally beyond the area 
occupied by the mouths. 
