REPORT ON CORALS—HELIOPORID. 123 
Characters of the Family HELIoporip&. 
A compact corallum present, composed of a fibro-crystalline calcareous tissue as in 
Madreporaria. Corallum consisting of an abundant tubular ccenenchym, and with 
calicles having an irregular number of lateral ridges resembling septa. Calicles and 
ccenenchymal tubes closed below by a succession of transverse partitions. Polyps com- 
pletely retractile, with tentacles when in retraction introverted. Mouths of the sacs 
lining the ccenenchymal tubes closed with a layer of soft tissue, but communicating 
with one another and with the calicular cavities by a system of transverse canals of 
soft tissue. 
Tubular Canenchym of Heliopora and its Homologies.—The structure of the 
ceenenchym of the Helioporide is entirely unique amongst Anthozoa; no other forms 
have a coenenchym composed thus of a series of long tubes packed side by side, and lying 
parallel to the calicular tubes and at right angles to the surface. It is to be remarked 
that the tubes are like the calicles in being open above, that they have walls composed 
in exactly the same manner as those of the calicles, and that they are closed below at 
intervals in the same way by exactly similar tabule. Further, the soft tissues lining the 
cavities of the ccoenenchymal tubes are identical in structure with those lining the 
calicular cavities, and the same transverse system of canals connects the summits of the 
tubes with one another, and with the summits of the calicular cavities, 
It seems by no means improbable that the ccenenchym here is composed of the 
tubes of aborted zooids (siphonozooids) which have lost the rudimentary organs, which 
they still possess in such a form as Sarcophyton, and have become mere tubular 
cavities, the openings of which to the exterior even have been obliterated ; it seems 
impossible otherwise to account for the presence of the succession of tabulz in the 
coenenchymal tubes. 
Fossil Allies of the Helioporidee.—The foregomg considerations are suggested by 
the circumstance that a series of fossil corals, grouped by Milne-Edwards under the 
Tabulata, appear most probably to have been Alcyonarians as well as Heliopora. 
The genus Chetetes was considered by Keyserling to have belonged to the Alcyon- 
arians, because of the absence of septa and the mode in which its polyps are 
grouped ; but Milne-Edwards retains it amongst the Zoantharians, because of its 
close resemblance to the Favositide, in which the presence of septa is regarded as 
conclusive in deciding against Alcyonarian affinity. The presence of calcareous 
septa, however, must now be considered a character of less importance than it formerly 
was. As is seen in the case of Heliopora pseudo-septa may exist, which do not 
necessarily correspond in any way, in disposition or number, with the membranous 
mesenteries. In the Favositide the septa seem to have been no more perfect than they 
