172 THE GREAT BARRIER REEF. 



characters possessed by Stylopora are the irregularly lobate and usually compressed contour 

 of the coral branchlets, and the distribution of the polyp-cells promiscuously instead 

 of in serial order. The corallites, moreover, possess, in addition to the twelve septa, 

 a conspicuously developed central style or columella. In company with those of Seriatopora, 

 the representatives of this genus inhabit the lowest level of the tide-exposed reefs, and 

 are among the species brought up from the greatest depths at which reef corals flourish. A 

 characteristic fragment of a living corallum of Stylopora palmata is included with that ol 

 Seriatopora in Plate VII. Stylopora pistillata and 5. digitata represent two other species of this 

 genus, that have been collected by the author on the Great Barrier Reef 



Pocillopora, the third genus in the group now under consideration, differs markedly in its 

 elements from both Seriatopora and Stylopora. In the abundant Barrier species, Pocillopora 

 damkornis, or a close ally thereof, the most symmetrically hemispherical coralla, present, in 

 their bleached condition, a not remote similitude to over-mature heads of a cauliflower or 

 broccoli. The ramifying branchlets into which the coralla are similarly subdivided, as com- 

 pared with those of Seriatopora and Stylopora, are irregular, somewhat thickened, and corru- 

 gate or angular at their extremities. The polyp-cells or corallites are also more closely 

 and irregularly crowded, and present only rudimentary traces of the septal elements. The 

 polyps of Pocillopora are, at the same time, indistinguishable in their external characters 

 from those of the last-named two genera, possessing, in a like manner, twelve short, distinctly 

 capitate, tentacles. The living colours of the coralla and polyps of the Barrier species are not 

 so brilliant as those ot Stylopora and Seriatopora. The extremities of the branchlets, and 

 also of the included polyps, are often a purplish-pink, but more frequently of a clear 

 brown. The distal ends and inflated tips of the tentacles are usually a darker tint of the 

 ordinary ground colour ; while, in many examples observed, the tentacle tops alone were a pale 

 beryl-green. The commonest Australian species, Pocillopora dainicortns, is plentifully developed 

 throughout the Barrier district, and usually occupies a low-level position on the tidally-exposed 

 reefs. The species growing in situ is included in many of the reef-views reproduced in this 

 volume, and notably in Plates XL, XII., and XV. of the photo-mezzotype series. Fragments 

 of coralla, with the extended polyps, are also represented in Figs. 3 to 3F of Chromo plate 

 No. VII. It commonly happens in some instances that a small barnacle of the genus 

 Pyrgoma, and in others a bivalve mollusc, allied to Pecten, affixes itself to the extremities of 

 this coral, causing it to become abnormally dilated and distorted in its efforts to cover in the 

 intruding organisms. Examples of such commensal attachment are illustrated by Figs. 3F and 

 30 of the plate last mentioned. 



All the corals hitherto described correspond structurally with one another, in that the 

 calcareous substance of their coralla, although often highly cellular, is not distinctly spongy 

 or perforate. On account of this character, they have been associated with the expressive 



