i6o THE GREAT BARRIER REEF. 



and the six erect ones pale primrose. Figures illustrating additional species of Galaxea are 

 included in Chrome No. 4, already named ; while the general aspect of the corallum as growing 

 in situ may be gained by reference to the photographic reef-view, Plate X2, wherein an 

 extensive colony-stock of Galaxea Espcri occupies a prominent position in the left-hand fore- 

 ground. The reef illustrated is adjacent to Stone Island, Port Denison, from which 

 point to the northernmost limits of the Great Barrier region various members of the genus 

 occur in abundance. An entire bleached corallum of the above-named most cosmopolitan type 

 of this genus is represented in Fig. 13 of the first of the series of photo-mezzotype 

 illustrations. 



The next coral group that invites attention is that of Mussa and certain allied genera. In 

 its simplest form, Caulastraea, the corallum much resembles that of Euphyllia, it being composed of 

 slender subcylindrical corallites, which increase in a similar manner by repeated bifurcation. It 

 is placed in a separate group, however, from Euphyllia, and the other types already enumerated, 

 in accordance with the characters of the internal radiating plates or septa, which, instead of being 

 perfectly smooth, or entire, are distinctly notched, or serrated. The character of the tentacles in 

 the living polyps of Caulastraea and its allies is also distinct from that of the Euphyllise, being 

 simply pointed or subulate, instead of distinctly knobbed or capitate. A figure of Caitlastraa 

 distorta, which has been obtained by the author at various localities, from the Warrior reef in the 

 north to the Palm Islands in the south, with the polyps expanded, is given in Fig. 2 of Chromo 

 plate No. V. The coloration of the living polyps, while not so brilliant as that of the Euphylliae, 

 is attractive. The external surface of the corallites varies from reddish to a bright golden-brown ; 

 the central or oral disk is a more or less brilliant green, and the surrounding fringe of subulate 

 tentacles is perfectly transparent. 



An advance of complexity in structure is presented by the genus Mussa. In the members 

 of this group the entire outer and inner surfaces of the component corallites bristle with spines and 

 serrations to such an extent, that they require careful handling. The names Mussa cactus, cardii/is, 

 dipsacca, Iwrrida, and spinosissima, which have been conferred on various members of the genus, 

 are of themselves amply indicative of their prickly character. The individual corallites in this 

 genus never present the even, subcylindrical, contour, characteristic of Euphyllia or Caulastraea ; but 

 their distal polyp-bearing ends broaden out into shallow cups two or three inches in diameter 

 and of the most irregular shape, such shape being, to a great extent, determined by that of the 

 abutting walls of the neighbouring corallites. These corallites, moreover, are rarely single, as in 

 the types previously enumerated ; two or more oral centres, representing conjoint polyps, being 

 most frequently included within the same corallite. This initial phase of complexity paves the 

 way to the still more intricate structural plan that obtains in the genus Symphyllia. 



The colours of the polyps in the genus Mussa somewhat resemble those of Caulastraea. 

 Brilliant green centres, with red-brown corallite rims and transparent tentacles, most frequently 



