On the Structure and Relations of certain Corals. lo3 



Family Helioporid^. 



A compact corallum present, composed of a fibro-crystalline 

 calcareous tissue as in Madreporaria. Corallum consisting of an 

 abundant tubular coenenchym, and with calicles having an irre- 

 gular number of lateral ridges resembling septa. Calicles and 

 ccenenchj-'mal 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 cavities by a system of trans- 

 verse canals. 



The structure of the coenenchym of the Helioporidae is entirely 

 unique amongst Anthozoa ; no other form has 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 tabulae. 

 Further, the soft tissues liniug the cavities of the coenenchymal 

 tubes are identical in structure with those liniug 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 coenenchym here is 

 composed of the tubes of absorbed polyps or zooids which have 

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

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

 openings to the exterior even have been obliterated ; 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 Alcj^onarians as well as Heliojiora. 



The genus Chcetetes was considered by Keyserling to have belonged 

 to the Ak\vonarians, because of the absence of septa in it, and 

 the mode in which its pol3'ps are grouped ; but Milne-Edwards 

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

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

 regarded as conclusive in deciding against Alcyonarian aflfinity. 

 The 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 Sti/laster and Cryptohelia 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 be 



Ann. iSc Mag. N. Hist. Ser. 4. Vol.xyn. 11 



