103 
— 
space, which has its internal wall formed by the innermost membrane and its external 
wall by an intermediate layer composed of the laterally-coalescent branches. The cells are 
situated upon the internal face of the outer layer of this central space (7. e. the interme- 
diate layer) ; and the two layers are kept apart by a system of pillars which are attached by 
their inner ends to the internal layer and by their outer ends to the intermediate layer. These 
pillars traverse the central space perpendicularly, and correspond with the fenestrules of a 
Retepora. The water must have been admitted to the central space, and thus to the cells, by 
openings in the free edge of the infundibuliform polyzoary, but none of our specimens exhibit 
this portion of the frond. 
In the genus Hemitrypa, (Phillips), the fenestrules do not perforate the frond so as to 
reach the outer face of the polyzoary, but are filled up by a calcified membrane. The cells, 
however, open upon the external surface, instead of into a central space, and the structure of 
the ccencecium is in other respects very different. 
The following is the only species of the genus which I have as yet’met with :— 
126. CRYTOPORA MIRABILIS (Nicholson). 
Cryptopora mirabilis, Nicholson, Annals of Nat. Hist., Feb. 1874. 
Polyzoary infundibuliform, apparently from one to three inches in height. External 
layer, thin, imperforate, smooth, or obscurely striated. Intermediate layer formed of the 
coalescent branches, marked by vertical grooves or sulci, which are placed about half’ a line 
apart, and sometimes bifurcate. Besides these grooves, the outside of the intermediate layer 
is marked by inosculating lines, which map out small oval or polygonal spaces-corresponding 
with the cells beneath. The inner surface of the intermediate layer carries the cells, which 
are arranged biserially in flexuous lines, and enclose oval or rhomboidal interspaces. These 
interspaces are disposed in very regular diagonal lines, about four in the space of two lines, 
and they give origin to a series of short rounded pillars which extend inwards at right angles 
to meet the internal layer. Central space in which the cells are situated about half a line 
to two-thirds of a line in depth. Internal layer thin and membranous. The entire frond 
springs from an exceedingly strong, horizontal, branched stalk, the surface of which is marked 
by vermicular striz. 
The materials in my hands are not sufficient to permit of an entirely full elucidation and 
illustration of the characters and structure of this remarkable species. Different specimens, 
however, or different parts of the same specimen, show the following appearances (Fig. 40) :— 
1. The external membrane is very thin, and is only preserved in part in -any specimen 
that I have seen. It corresponds with the reverse or non-poriferous layer of an ordinary 
Retepora, and in reality is to be regarded as nothing more than the exterior portion of the in- 
termediate or celluliferous layer. Nothing, in fact, is commoner than to meet with precisely 
similar specimens of Refepora in which the reverse has been stripped off, and the bases of 
the cells are thus exposed to view. 
2. The intermediate layer (together with the external layer, as just remarked) is clearly 
formed by the coalescence of the branches. When viewed from the outside (Fig. 40, #. 6) it 
exhibits shallow vertical grooves marking out the original branches, and it also shows the 
outline of!’ the cells below. 
3. The structure of the interior of the intermediate layer, and of the central space -of 
which it forms the outer boundary, can be studied in specimens which exhibit the inner sur- 
face of the funnel, or in those which have been broken across transversely. In specimens 
which show the interior, and from which the innermost layer bas been removed in whole or 
in part, we see the mouths of the cells, as rounded pores placed on the inner aspect of the 
intermediate layer (Fig. 40 D). The cells are arranged in double rows, forming regularly 
bent or undulating lines, which correspond with the inner faces of the branches, and which 
enclose the oval spaces which correspond with the fenestrules, just as in Refepora. When we 
look, however, at a specimen which is broken across (Fig. 40 /.), it is seen that instead of 
perforations between the inosculating branches, we have a series of stout pillars, which run 
perpendicularly inwards from the poriferous face, and have their internal ends connected 
together by a thin caleareous membrane, which forms the innermost lining of the funnel- 
shaped frond. There is thus formed a continuous central space, which is lined outwardly by 
the cells, and to which water must have been admitted by the opening in the margin of 
the funnel. 
