1 64 THE GREAT BARRIER REEF. 



Plate V. of the chromo-lithographic series. The polyps, as is the case in the genus 

 Goniastrsea, possess innumerable subulate colourless tentacles that correspond in number with 

 its septal divisions, and expand chiefly at night. Figures 5 and 8 of the plate above 

 referred to depict other brilliantly-coloured members of the genus Prionastraea whose specific 

 identity has not yet been satisfactorily determined. In the one instance, the polyp centres 

 are grass-green and the septal ridges dark brown ; in the other, lilac-brown polyp centres 

 are associated with bright sage-green septal ridges. 



In the same manner that the corallum of the genus Symphyllia, with its coarsely spinous 

 undulating valleys and ridges, has been shown to be structurally related to that of Mussa, the true 

 Brain-stone corals represented by the genus Coeloria, Leptoria, Meandrina, and a few other allied 

 forms may be demonstrated to be structural modifications only of the genera Goniastrsea, Prion- 

 astraea and their allies. In Goiiiasfrcea Grayi it may, in fact, be frequently observed that three or 

 four of the corallites, or polyp centres, in place of being separated by their septal ridges, have 

 remained united in a linear series. The repetition of this phenomenon on so extended a scale as 

 to embrace as many as a dozen or more of the constituent corallites, united in branched or 

 sinuous lines of variable length, would produce a structural pattern, similar to that which obtains in 

 the genus Coeloria. Like Goniastraea, Coeloria enters very extensively into the composition of the 

 Great Barrier reefs, and may be recognised as occupying conspicuous positions in many of the 

 photographic views reproduced in this volume. Among these. Plates III., VII., and VIII. of the 

 photo-mezzotype series maybe specially cited, as including in their foregrounds large hemispherical 

 masses of the commoner species, which is apparently identical with Coeloria sinensis. Like the 

 Goniastraeae, the Brain-stone corals enjoy a cosmopolitan distribution throughout the Barrier 

 district, and are among the earliest to be uncovered by the receding tide. Although the common 

 specific form last named, like Goniastrwa Grayi, is usually either a sombre or a golden-brown 

 hue, there are several allied types that exhibit a marked diversity of colour. In one species, allied 

 to Cceloria Esperi and C. arabica, the valleys, or polyp-furrows, are dark violet, and the intervening 

 septal ridges golden-brown. In another variety of the same species, the septal ridges are amber- 

 coloured and the polyp-furrows pale green ; while in a third species of apparently the same 

 type, the septal ridges are dark brown, and the polyp centres either pale aquamarine or sage-green. 

 In yet a fourth variety of the same, or of a very closely-allied species, the corallum is a light sage- 

 green throughout. In a fifth local variety, obtained only from the Palm Islands reefs, the narrow 

 septal ridges are light brown, and the wider intervening polyp-furrows a dark bottle-green. The 

 colours here enumerated are characteristic of the coralla in their living condition, with the polyp- 

 tentacles retracted, as obtains when the tide recedes from the reefs, or even when the coralla are 

 covered by water in full daylight. The expanded tentacles in all the species observed were either 

 entirely colourless, or reproduced the palest shade of the same tint as the adjacent polyp centres 

 Figures, illustrative of the retracted living aspect of some of the most characteristic of the 



