REPORT ON CORALS — HELIOPORIDyE. 123 



Characters of the Family Helioporime. 



A compact corallum present, composed of a fibro-crystallme 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 Ccenenchym of Heliopora and its Homologies. — The structure of the 

 ccenenchym of the Helioporidse is entirely unique amongst Anthozoa ; no other forms 

 have a ccenenchym 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 tabulae. Further, the soft tissues lining the 

 cavities of the ccenenchymal 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 tabulae in the 

 ccenenchymal tubes. 



Fossil Allies of the Helioporidae. — The foregoing 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 Chcetetes 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 Favositidse, 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 Favositidaj the septa seem to have been no more perfect than they 



