CORALS AND CORAL REEFS ^VAUGHAN. 



195 



corals to their environment with an account of conditions there. 

 The following table shows the relations: 



Relations of groicth-form of Coros-Kccling corals to hahitat. 



Within the lagoon free corals or corals that form fragile branches 

 or folia are predominant ; on the barrier flat and in the barrier pools 

 the forms with stronger skeletons are more numerous; while on the 

 exposed barrier there are only corals that have a massive growth- 

 form or are composed of stout branches. One of the species, Pocillo- 

 pora elegaTis Dana, which forms compressed branches, occurs within 

 lagoons and on barriers. The branches of the specimens in the 

 lagoon are tall and rather weak, while specimens on the barrier have 

 the branches aborted into slightly protuberant nodules. Plate 6 illus- 

 trates a corallum of the lagoon kind, and plate 5, figure 2, illustrates 

 a specimen Dr. Wood Jones collected on the Cocos-Keeling barrier. 



Six specimens of Pocillopora hulbosa Ehrenberg taken by Dr. 

 Wood Jones from a floating log are very interesting in this connec- 

 tion (pi. 5, fig. 1). He says regardim^ these specimens: 



In the lagoon, a large portion of a tree trunk was floated, and made fast 

 to an anchor and chain ; the wood was used to float a ship's moorings, and re- 

 mained just two years in the water. When it was removed in 1906, several 

 colonies of Pocillopora had started growths upon it, and they had taken up 

 different positions around its circumference. The colonies growing above were 

 flattened bosses ; those on the sloping sides showed more tendency to branch ; 

 and those below its convexity were delicate branched forms. 



Now the environments of these colonies were very different, and they were 

 absolutely constant. At all stages of the tide waves broke upon its upper sur- 

 face, whilst the sides were in gently moving unbroken water, and the bottom 

 was in comparative calm. * * * 



Dr. A. G. Mayer made a very interesting collection of corals at 

 Murray Island, Australia, and I have described them in my paper 

 above cited. Preceding my paper, Doctor Mayer has given in the 

 same volume an account of the ecology of the Murray Island reef, in 

 which he presents a statistical statement of the number of coral 

 colonies according to species in successive squares across the reef. I 

 based the following table on Doctor Mayer's collection: 



