122 THE VOYAGE OF H.M.S. CHALLENGER. 



seems to differ from all other Alcyonarians except Corallium. From both Corallium and 

 Tubipora, Heliopora differs in that the hard tissue of its corallum shows no signs of 

 being composed of fused spicules, but in its histological structure most closely resembles 

 Zoantharian corals. With the Milleporidse and with Pocillopora and Seriatopora 

 Heliopora is allied solely on account of its possession of tabulae, and these structures 

 being possessed alike by Hydrocorallinas, Helioporidse, Tubiporidae, and certain Madre- 

 poraria, their presence is proved to be of no classificatory importance, and is of less 

 value even than Professor Verrill showed it to be. The group Tabulata must be 

 entirely given up as only misleading in its signification, and the corals formerly placed 

 in it must be distributed amongst their natural allies. There can hardly be a doubt that 

 Seriatopora will prove to be, like Pocillopora, a Zoantharian. Heliopora thus stands 

 quite alone amongst modern forms ; and in the peculiar structure of its cellular 

 coenenchyin it is so remarkable that it is unlikely that on examination of the soft parts 

 of other living corals, at present known from their coralla only, any near relatives of it 

 will be discovered. Amongst extinct forms, however, Heliopora has several close allies, 

 and the genus itself existed in the Cretaceous period. The genus Polytremacis differs 

 apparently only in the more perfect development of the so-called septa, which reach to 

 the centres of the tabulae. The genus occurs in the Chalk, Greensand, and in Eocene 

 formations. Heliopora has, further, a very closely allied palaeozoic representative in 

 Heliolites, in which the ccenenchymal tubes are provided with very closely placed 

 tabulae. Professor Alleyne Nicholson 1 groups with these Plasmopora, Propora, Lyellia, 

 and Pinacopora ; he finds a difficulty in the fact that the cavities of the tubes do 

 not communicate with those of the calicles in Heliolites, and appears not to have 

 understood my description of the manner in which the polyp cavities communicate 

 with the sacs of the tube cavities in Heliopora. There are no apertures in the walls 

 of the calicles, or tubes in Heliopora, any more than in Heliolites, and the connecting 

 canals pass, as described, only over the edges of the mouths of the ccenenchymal tubes, 

 lying cpiite superficially. 



The three genera Heliopora, Polytremacis, and Heliolites differ from one another in 

 so slight a degree that they are placed under the one genus Heliopora by Queenstedt. 

 For the reception of the genus Heliopora and its fossil allies I formed a separate family 

 of Alcyonarians characterised as follows from the recent species. 



1 H. Alleyne Nicholson, On the Structure and Affinities of the Tabulate Corals of the Palaeozoic Period, Edinburgh, 

 1879, pp. 242, 243. 



