DESCRIPTION OF CHALK CORALS. 293 
sidered as effects of unequal abrasion ; and not due to the occurrence so near 
the surface of young cavities. All attempts failed to discover the precise point 
in the older tubes whence the young issued; but the great extent to which the 
cavities overlaid each other indicated that the development must have taken place 
towards the lower extremity of the parent tube. Not a vestige of a transverse 
plate was detected, the dimensions of the mature visceral receptacles not exceeding 
the requirements of an ascidian polype’s digestive organs ; and when once attained, 
no subsequent extension was made. It is not meant that the absence of transverse 
plates proves an extinct coral does not belong to the class Anthozoa, as they 
are wanting in true Alcyonie ; nevertheless they are either present or wholly de- 
ficient throughout a genus of that great group; whereas, if the chalk coral were 
considered an Apsendesia, they would be absent or present according to the 
species. Moreover, the essential characters of Mr. Dixon’s zoophyte are totally 
dissimilar from those of Alcyonide, and are much more nearly allied to the con- 
stituents of an ascidian than an anthozoan polype. Whether structures similar 
to those mentioned above exist in Aps. dianthus remains to be ascertained: they 
certainly do not occur in Aps. cerebriformis ; but the characters of the genus de- 
pend solely on the composition of Lamouroux’s type and only species. It has 
been already stated, that a small amount of agreement is apparent between the 
cretaceous fossil and Aps. cristata, the points being a somewhat analogous mode 
of branching, regarding the crests as representatives of branches, and in pores 
occurring on the back of the ramifications as well as on the front ridge, though 
in both cases to a limited extent (Icon. Zoophyt. pl. 55. figs. 5b, 5c). On the 
contrary the differences are many. It would appear from the published descrip- 
tions, that apertures are totally wanting on the sides of the pseudo-branches, and 
M. De Blainville alludes to the peculiarity of their existence in analogous por- 
tions of Aps. dianthus ; but in the chalk coral they abound everywhere except 
along a non-persistent middle line ; again, nothing resembling the dorsal layer to 
the leaf-like expansions of Aps. cristata occurs in Mr. Dixon’s fossil, an import- 
ant difference when the general composition of the two polypes is considered ; 
still further, no allusion is made by the authorities quoted to a plate, whereby the 
mouth was progressively narrowed and occasionally at least obliterated, though 
such a structure, as before stated, characterizes the chalk zoophyte ; lastly, if 
Apsendesia cristata be truly an Anthozoon, then no identity respecting even the 
class can exist. Leaving however that point open to inquiry, the other differ- 
ences are believed to be fully sufficient to warrant the inference, that the chalk 
fossil should not be regarded as an Apsendesia ; and it is conjectured that Aps. 
2a 
