DESCRIPTION OF CHALK CORALS. 24) 
thirty-two examples, many of which had well-preserved terminations, only one 
exhibited traces of the character, and it afforded other peculiarities. So far there- 
fore as this component part is concerned, the fossils generally which are assigned 
to Cary. centralis, cannot be regarded as Cyathine. 
The internal composition of Cya. cyathus is unknown to the compiler of these 
memoranda; but in a coral believed to be a distinct species of similar dimen- 
sions, transverse plates between the lamellz were wanting ; and though a union 
of two of the latter was noticed in one instance, yet such a junction could not 
be regarded as an equivalent structure. They were also absent in the largest, 
longest specimens of Cy. Smith. On the contrary, they formed a prominent 
structure in the chalk fossil (Tab. XVIII. fig. 3) wherever the interior was ex- 
posed. With respect to the proportion of the exterior covered by the animal, 
the extinct coral apparently differed also from the recent. Of thirty-two speci- 
mens examined, seventeen were encrusted by marine bodies; and five of the 
seventeen exhibited clear evidence of affixed zoophytes having been coated by 
coral secretions, and the added matter was not limited to a particular part, but 
was spread evenly and continuously thinning off upwards. It is therefore evident 
that the animal had the power of contracting and extending, and possibly at 
somewhat distant intervals of time. The absence of encrusting bodies cannot 
however be received as a proof of an investment by the polype, depending clearly 
on extraneous circumstances ; nor can their presence, except in cases similar to 
that just mentioned, as it is often difficult to determine, especially in organic re- 
mains, whether the incrustation took place during life or subsequently ; and the 
only conclusions which can be drawn regarding the cretaceous fossil are,—-|st, 
that the exterior was not wholly and permanently covered by animal matter ; 
and 2ndly, that the extension was not so uniformly restricted as in Cyathina. 
The recent genus evidently could not thicken the outer surface after the first 
perfecting of the wall; and in the fossil coral the coating varied in amount, or 
was in some cases not perceptible. About twenty specimens had plainly additions, 
while ten gave no indication of increase ; and both the thickened and unthickened 
were regular as well as irregular in growth, and differed not in composition. If 
the coral which is considered a new species of Cyathina exhibits truly the 
characters of the genus, a decided filling up of the lower portion occurs. The 
total height of the specimen was 1} inch, the depth of the terminal cup 7 lines, 
and the centre preserved its reticulated composition 3 lines lower ; but throughout 
the remaining 8 lines, that structure was solidly filled up, as well as the intervals 
between the lamellz to a great extent. Cy. Smithii afforded no proof of a central 
