DESCRIPTION OF CHALK CORALS. 251 
productions appears to have been the formation of a lamellated zone around the 
mound (figs. 28, 27 mag.), one of those peculiar increments before mentioned. 
This early step was not accompanied by an upward extension, the outer structure 
being based on the general surface of the coral. After a time the two areas probably 
blended by growth into one, the diameter of somewhat elongated simple cavities 
being about equal to that of the mound and zone united (fig. 17 magnified in 
same proportion as fig. 26). In further advancements no differences, it is pre- 
sumed, occurred in the growth of pallial and marginal developments, or between 
them and the upward extension of the primary cavities, but that all progressed 
by the same general law, and by successive stages of lateral expansion, more or 
less visible in the hollows from which the lamellz had perished. 
The lamellz afford a further distinction ; they agree with those of true Ocu- 
line by exceeding twelve in number’, but they do not pass solidly into the struc- 
ture surrounding the cavity ; while in the recent genus they range in all species, 
it is believed, into that portion of the coral. The interior of the largest cavities 
(fig. 14), which had lost their lamelle, exhibited no fractured, perpendicular edges, 
but faint ridges and furrows, roughened only by the peculiar texture of the coral, 
and therefore proved, it is conceived, that the removal of the lamell was owing 
to a want of solid union with the wall, and not to disruption. Sometimes, par- 
ticularly in young pallial developments, a perfect junction existed between the 
lamellz and the then existing boundary, and even in more advanced states there 
was an apparent junction. The structure forming the circle to which the lamelle 
were united, is believed however to have been developed by portions of the 
polype differently constituted from those which produced the general body of the 
coral, including the permanent boundary of the cavities. Thus, the partially 
preserved, mature hollows (fig. 20) had a slight interval between the lamellz 
edges and the surrounding solid substance of the coral, indicating the removal of 
a thin perishable layer ; and where the decay was less (fig. 25), the position of 
the interval was occupied by a structure intimately blended with the lamella, and 
filling also to a limited extent the space between them: in some cases likewise 
single plates occurred in contact with the permanent boundary, or were united to 
it by minute points, decomposition having taken place more rapidly between the 
lamelle, than between the edges of the latter and the undecaying periphery. The 
inner perishable composition was evidently produced by structures immediately 
‘ Consult De Blainville’s genus Dentipora, Man. d’Actinologie, p. 382, and M. Milne-Edwards’s 
remarks on Oc. virginea, 2nd edit. Lamarck, t. ii. p. 455, for species with less than twelve. 
