7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 51 



and Titrb. Lonsd. floriformis is represented in an almost unchanged condition 

 in Astroides calycularis. 



In describing the growth stages of Parasmilia Lang( 2 ) points out that the 

 constrictions which arise periodically iu the growth of the corallum mark 

 points in the life of the coral where fresh growth took place after a period of 

 rest and that at such a rejuvenescence the coral recapitulates its earlier growth 

 phases in a condensed form, which the author regards as evidence that the 

 rejuvenescence is a form of fission. 



According to Taylor the Archseocyathinse were compound organisms whose 

 internal structure - - both as regard composition and regularity - - approximates 

 to that of the Anthozoa, but whose general shape, protean forms, and methods 

 of attachment resemble the Porifera. This family is of equal rank with, and may 

 represent a link between, the Porifera and Coelenterates. 



Andrews concludes, from a consideration of the coast features of Queensland, 

 that in Pliocene times an elevation carried the Tertiary and Cretaceous plains 

 3000 feet above their former positions. The subsidence which determined the 

 present Barrier Reef may be referred to Pleistocene times, and the latest 

 coastal elevation to the historical period. 



Hedley & Taylor studied the Great Barrier Reef, near Cooktown, and find 

 that the growth of a reef proceeds in a regular cycle. If the reef reaches 

 the surface with its axis along the wind its shape endures, but if across the 

 wind, then its ends are produced backwards, forming first a crescent, lastly an 

 oval enclosing a lagoon. Descent at this stage arrests development or rejuve- 

 nates the reef. In quiescence the lagoon walls broaden, the lagoon is obliterated, 

 a vegetated sandbank spreads on the summit and the atoll, now a cay, is mature*. 

 Negro-heads are not relics of raised reefs, but are tossed up by hurricanes. 

 The authors agree with the Darwinian view of the origin of atolls, because 

 Queensland shows subsidence in (1) drowned river mouths, (2) the formation of 

 its bays and islands, and (3) the sinking of the isthmus which once joined 

 Cape York to Papua. The sinking here is part of a general movement which 

 affected the whole of E. Australia and Tasmania. The Barrier does present a 

 steep outward face, thus agreeing with the Darwinian hypothesis. The ejections 

 from the Murray volcano show coral formation to occur there at considerable 

 depths; the maturity* of the northern reefs indicates slow subsidence followed 

 by quiescence. 



Jones, as a result of observations on Cocos Keeling atoll, suggests that the 

 process of sedimentation takes the largest share in the production of an atoll. 

 Sediment is deposited as ridges or banks which can not go beyond a certain 

 plane because of the levelling action of the waves. The bathymetrical limit of 

 the reef-building corals is intimately associated with this limiting plane of sedi- 

 mentation, whose depth varies with the local conditions of the sea. Luxuriant 

 corals would not occur below this plane because sediment would fall on the 

 zooids. But sediment may build up banks to this line and reef corals 

 build from this line to the surface. Probably deep-water algae, corals, etc. 

 with calcareous skeletons first populate the bank. Reefs so formed tend to 

 become basin-shaped and to develop as flat banks with raised edges and 

 abundantly covered with coral colonies. The chief factor is sedimentation: 

 suspended matter is deposited on the surface of the coral colonies but at the 

 edges is more readily washed off by the waves, therefore the corals flourish 

 best here. Similarly a colony of Porites in a quiet pool grows first as a spherical 

 mass; when its upper surface becomes large enough to afford a lodgment for 

 sediment this injures the central zooids and the peripheral ones grow faster; 



