On the Struchire and Relations of certain Corals. 1.0-5 



Family Helioporid.^;. 



A compact corallum present, coDiposed of a fibro-crystalline 

 calcareous tissue as in Madreporaria. Corallum consisting of an 

 abundant tabular coenenchym, and with calicles haviug an irre- 

 gular number of lateral ridges resembling septa, Calicles and 

 coenenchymal tubes closed below by a succession of transverse 

 partitions. Polyps completely retractile, with tentacles when in 

 retraction introverted. Mouths of the sacs lining the coenenchymal 

 tubes closed with a layer of soft tissue, but communicating with 

 one another and with the calicular canties by a system of trans- 

 verse canals. 



The structure of the coenenchym of the Helioporidjie is entirely 

 unique amongst Anthozoa ; no other form has a coenench}Tn 

 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 coenenchymal 

 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 ca\'ities. 



It seems by no means improbable that the coeuench\Tn here is 

 composed of the tubes of absorbed polyps or zooids which ha\e 

 lost the rudimentary organs, which they still possess in such a 

 form as Sarcophyton, and have become mere tubular cavities, whose 

 openings to the exterior even have been oblitei-ated ; it seems 

 impossible otherwise to account for the presence of the succes- 

 sions of tabulae in the coenenchymal tubes. The foregoing con- 

 siderations are suggested by the circumstance that a series of fossil 

 corals, grouped by M,-Edwards under the Tabulata, appear most 

 probably to have been Alcyonarians as well as Ucliopora. 



The genus C%ftetes was considered by Keyserling to have belonged 

 to the Alcyonarians, because of the absence of septa in it, and 

 the mode in which its polyps are grouped ; but Milne-Edwards 

 retains it amongst the Zoantharians, because of its close resem- 

 blance to the Favositidie, in which the presence of septa is 

 regarded as conclusive in deciding against Alcyonarian atfiuity. 

 'J^he presence of calcareous septa, however, must now be con- 

 sidered 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 St i/ luster awA Crj/ptohelia the 

 calcareous septa are obviously formed as infoldings of the margin 

 of the calicles. Here the septa are between, instead of opposite 

 to the tentacles ; and membranous mesenteries appear to bo 



Ann. (& Mag. N. Hist. Ser. 4, Vol.wW. 11 



