CORALS AND CORAL-ANIMALS. 163 



throughout their peripheral edges. The genus Goniastraea, which represents one of the 

 most numericall}^ abundant constituents of the high-level and shoreward edges of the Barrier 

 reefs, furnishes an appropriate illustration of this series. Goniastrcea Grayi, the commonest 

 Australian species, is conspicuously en evidence in a considerable number of the reef-views 

 reproduced in this volume, and will be found to exhibit a considerable diversity of contour. 

 A near view of a typical colony-stock of this coral will be found in the foreground of Plates II. 

 and III. of the phototype series, occupying the left-hand side in the first, and the right-hand one 

 in the second plate, and representing, as a matter of fact, opposite aspects of the same corallum. 

 Being so much in the foreground, every individual polygonal corallite, or polyp centre, of the 

 compound structure is here distinctly visible. Another example in which, in the middle and 

 farther distance, the same species is so abundant that its rounded coralla present somewhat the 

 appearance of a flock of sheep is furnished by Plate V., No. 2. Examples in which the coralla 

 form almost perfect .spheroids are illustrated by Plates VI. and X., while in Plate XIV. a 

 very singular departure from the normal growth occurs. In this instance, somewhat towards 

 the left in the middle distance, a corallum of a type allied to Goniastrcea eximia has been so 

 indented, or interrupted, in the course of its natural growth that it presents the most grotesque 

 resemblance to a human head. A descriptive account of this remarkable reef is given on 

 page 24. 



The living colours of Goniastrcea Grayi, referred to in the foregoing paragraph, and illus- 

 trated by Fig. 21 of the Chromo-lithographic Plate No. V., are either a dark liver- or a golden- 

 brown, no brighter tints having been in any instance found associated with it. In the second 

 species, named Goniasfra-a eximia, which frequently grows close beside G. Grayi, the immediate 

 centres of the polygonal corallites are often pale green, and the surrounding septal edges light 

 brown, or in rarer instances pale pink or lilac. The coralla of this species are much more 

 irregular in shape than those of Goniastraea Grayi, being usually divided up into smaller lobate 

 segments. A typical illustration of a reef on which this species represents the dominant type is 

 furnished by Plate IV., No. i, wherein is delineated the foreshore area of one of the most 

 characteristic fringing-reefs of the Palm Islands. 



Among the many species of Barrier Star-corals, or Astraeaceas, that agree very nearly in 

 structure with the Goniastraeas, there are some few which are noteworthy, on account of their 

 brilliant coloration. The genus Prionastrasa is especially conspicuous in this association. In one 

 species in particular, P. robiista, the coralla, in the living state, vary in hue from the most brilliant 

 emerald-green to straw-colour, with equally brilliant green oral centres ; or, again, they may be 

 straw-colour or light buff throughout. In place of forming sub-globose or evenly-rounded colony- 

 stocks, this generic type produces coralla which are usually partly encrusting and partly raised 

 in the form of irregular angular outgrowths. Delineations of the characteristic aspect of two 



diversely-tinted living coralla of Prionastrcea robnsta are included in Figs. 15 and 16 of 



Y 2 



