1875.] Structure and Relations of certain Corals. 65 



The three genera Heliopora, Polytremacis, and Heliolites differ from 

 one another to so slight a degree that they are placed under the one 

 genus Heliopora by Quenstedt. To include these three genera, a new 

 family of Alcyonarians must be formed, for which the term Helioporidae 

 appears most suitable, which family may from the recent species be thus 

 characterized : — 



Family Heliopoeid^:. 



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 irregular 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 communi- 

 cating with one another and with the calicular cavities by a system of 

 transverse canals. 



The structure of the coenenchym of the Helioporidse 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 

 tabular. 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 cavities. 



It seems by no means improbable that the coenenchym here is com- 

 posed of the tubes of absorbed polyps or zooids which have lost the 

 rudimentary organs, which they still possess in such a form as SarcopJiy- 

 ton, and have become mere tubular cavities, whose openings to the ex- 

 terior even have been obliterated; it seems impossible otherwise to 

 account for the presence of the successions of tabulae in the coenenchymal 

 tubes. The foregoing considerations 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 Heliopora. 



The genus Chcetetes 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 resemblance to the Favositidse, in 

 which the presence of septa is regarded as conclusive in deciding 

 against Alcyonarian affinity. The presence of calcareous septa, how- 

 ever, 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 



VOL. XXIV. E 



