CORALS AND CORAL-ANIMALS. 177 



fringing reefs of Stone Island, Port Denison, as to represent, locally, the chief living coral- 

 constituent of the reef The important position occupied by this species, in the locality referred 

 to, is well exemplified in the photographic reef-view reproduced in Plate X., No. 2. As 

 indicated in this illustration, the growth-plan in this species takes the form of erect vertically 

 compressed folia, which coalesce with one another at various angles, and so constitute encrusting 

 masses of indefinite extent, which, on account of their peculiar structure, possesses great 

 rigidity combined with apparent lightness. The living colony-stocks of the Port Denison 

 growths of this Lophoseris, as represented in Chromo plate VII., Fig. 11, usually possess a 

 ground tint of cream or light-stone colour, the polyp centres being represented by pale green 

 or lemon-yellow radiating stars ; the polyp tentacles, when extended, correspond in colour 

 with the septal radii. In other localities, such as Adolphus Island, Torres Strait, and else- 

 where, the living coralla of an allied but more massive species, Lophoseris crassa, observed by 

 the author, were a rich golden-brown, and the radiating centres and extended polyps bright 

 grass-green. 



The third generally recognised subdivision of the Stony-corals, known as the Madrcporaria 

 perforata, includes all those forms in which the calcareous substance of the corallum is of a 

 distinctly porous nature. In its variety of species, and in the numerical abundance and dimen- 

 sions of the individual colony-stocks belonging to this group that enter into the composition 

 of the Great Barrier coral-reefs, it claims equal rank with the tribe of the Astraeaceas previously 

 described. On many of the tidally-exposed reefs, as a matter of fact, its members monopolise 

 by far the largest area of the visible reef-scape ; and in one genus, Porites, they represent 

 the foundation of the outer breastwork of the reefs that are exposed to the full brunt of the 

 raging breakers. 



Beginning with the simplest, and proceeding in the direction of the more complex 

 members of the group, there are several Madrcporaria perforata that correspond with an 

 ordinary Mushroom-coral, in that they are the equivalent of a single individual polyp. In 

 one of these, the genus Balanophyllia, which has a British representative, the corallum is 

 short, subcylindrical, and permanently rooted to the coral-rock or other selected fulcrum. In 

 an allied Great Barrier type, Heteropsammia Michcliiii, the corallum is remarkable for attaching 

 itself in the earliest stage of its growth to the shells of small gasteropodous molluscs, which, 

 in course of time, it completely enshrouds with the substance of its corallum ; and thence- 

 forward it exists as a sub-globose independent coral, of about three-quarters of an inch in 

 diameter. This generic form necessarily plays no material part in the process of reef con- 

 struction ; and it is usually procurable only with the assistance of the dredge. It has been 

 collected by the author both in Cleveland Bay, off Townsville, and in the neighbourhood of 

 the Capricorn reefs ; and an illustration of this somewhat singular type, in which the polyp 

 tentacles are fully extended, is given in Fig. 12 of Chromo plate VI. 



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