250 DESCRIPTION OF CHALK CORALS. 
margin of the parent ; and by the other, in the mantle, and often at a consider- 
able distance below the extremity. In the first mode (figs. 14, +, 18, +, 21) the 
cavity was progressively advanced as the wall of the previous structure extended 
upwards ; and the young additions were not limited to one or two, nor to a 
particular side of the parent hollow, or to a single period of its growth; more 
than two having been noticed, irregularly situated, and either on the margin or, 
when perfected, below it. This progressive plan of formation distinguishes the 
fossil from Oc. pallens of Ehrenberg (Oc. hirtella, Lamarck, Esper, Madrep. tab. 14), 
and possibly other species, in which the young cavity is produced in the sub- 
stance of the animal matter investing the top of the branch, and simultaneously 
around the whole of the incipient area; while in the chalk zoophyte the process 
agrees with that observable in Dendrophyllia ramea (De Bl.) ; but with this differ- 
ence, that in the recent coral there is not a perfect, early disconnection between 
the interior of the older cavity and that of the offset, whereas in the extinct a solid, 
continuous wall cuts off immediately all direct communication. Occasionally, 
where the lamellz had perished, an irregular hole appeared at the base of the 
side shoot, but it was plainly due to fracture or decay. The second process was 
seated in the investing mantle, and, as before stated, often considerably below 
the extremity of the stem or branches; and these young abdominal receptacies 
were distinguished from the others, by their less size and indistinctness, as well 
as by the development, however imperfect, being contemporaneously effected 
around the area. The earliest observed stage of this second process (fig. 24, mag.) 
presented a small conical mound, about a line in breadth, of variable form, and 
with an irregular opening, in which traces of lamelle were visible. Some of 
them seemed to have a partial, and others a perfect solid covering ; but as an 
absorbing power among Anthozoa is believed to be unknown, and as cavities 
which had attained maturity with some upward growth were also occasionally 
coated over, it was inferred, that the polype structures of those incipient fabrics, as 
well as of the more advanced, had perished prematurely, and that the mounds had 
been overlaid by a layer of coral matter secreted from the mantle. Similar cover- 
ings may be noticed in cavities of Oculine from which the abdominal structures 
have been removed by accidental destruction. An advanced step in these pallial 
the additions along the hemispherical margin of the coral, consisting first of limited ares, afterwards 
of semicircles and ultimately of circles, according as the general polype substance grew; and the 
young hollows within the area of a specimen are simultaneously formed around their whole circuit, 
being produced in the midst of animal structures. 
