CORALS AND CORAL-ANIMALS. 185 



photographically' reproduced in Plate XI. ; one erect, and another overturned, corallum, occupying 

 a position near the centre of the middle distance. The colours of the living coralla and polyps 

 of the Montiporae are almost as brilliant as those of the genus Madrepora. The species 

 illustrated in Plate IX. is usually a bright lilac, and the polyps a deeper violet. In some instances 

 the corallum is light brown, bordered with mauve, and the polyps are dark green; and in others 

 the corallum is brown, edged with bright yellow, and the polyps are greenlsh-vvhite. In a fourth 

 variety the general surface of the corallum is a light golden-yellow, and the associated polyps 

 are brilliant violet. Coloured illustrations of several of the more prominent foliaceous species 

 of the Barrier Reef Montiporas are included in Chromo plate No. VIII. As indicated in the 

 figures there reproduced, the living polyps in this generic group are exceedingly minute; and 

 the tentacular elements are in most instances altogether rudimentary, and represented by mere 

 inflated papillae. One of the more massive species of this genus, allied to Montipom scabrictila, 

 is delineated in Chromo VI., Fig. 11. It forms castellated or tufted masses a foot or more 

 high, the basal portions of which are, in life, nearly black, virhile the terminal areas are light 

 brown or cream-coloured. The twelve rudimentary bulbous tentacles are usually of a clear 

 brown. 



With regard to the ivlc played by the Madrcporaria perforata in the task of solid 

 reef-construction, the palm must, undoubtedly, be awarded to the genus Porites. The indi- 

 vidual corallites and the associated polyps of the species of this genus are among the most 

 minute of their class; but they form aggregations that in dimensions and density surpass 

 those of any other type. One of the commonest species of the genus, Porites astrceoides, not 

 unfrequently builds up coralla that measure over twenty feet in diameter and as many in 

 height, the whole fabric being the product of repeated subdivision and multiplication of a 

 single primary polyp, of microscopic dimensions. These huge, massive, Porites grow in 

 the deep water on the outer edges of the reefs, and commonly form a basis for smaller, 

 higher-level, corals. Instructive illustrations of the plan of growth of these massive forms 

 are afforded by the photographic views that constitute the lower figures of Plates Nos. V. 

 and VI. In the latter of these, delineating a portion of the fringing reef of the Greater 

 Palm Island, the irregularly lobate masses of the Porites show indistinctly beneath the water- 

 level, and are surmounted by a luxuriant colony of other coral species, including members 

 of the genera Goniastraea, Symphyllia, Madrepora, Mussa, and Coeloria, many of wnich are 

 themselves of considerable dimensions. The long diameter of this huge Porites corallum is 

 not less than thirty feet, and the depth of water along the edge exposed to view is over two 

 fathoms. A corresponding growth of this same species of Porites is illustrated in the reef- 

 views reproduced in the upper figures of Plates VI. and X. of the same phototype series. The 

 substratum of the reef on the outer end of Vivien Point, Thursday Island, illustrated by Plate II., 

 and referred to at some length at pp. 7 et set/., in connection with systematic measurements 



B 15 



