202 THE GREAT BARRIER REEF. 



collected by the author in the Barrier area ; and two of them form such substantial coralla as to 

 represent a conspicuous feature in the coral landscape. In one of these species, Millcpora 

 alcicornis, the corallum takes the form of a thick bush-like aggregation of flattened palmate, or 

 frondose, expansions, all of which are disposed in the same vertical plane. This species is 

 very characteristically represented in the photographic reef-view reproduced in Plate VII., 

 wherein it occupies a prominent position, in mid-distance towards the right-hand side. The 

 second species of the genus, Millcpora ramosa, forms cylindrical, dichotomously branching, 

 shrub-like coralla, much resembling those of many ordinary Stags'-horn corals of the genus 

 Madrepora. This species, which is rarely uncovered at ebb-tide, is very abundantly repre- 

 sented in Plate X., No. i, illustrative of a portion of the fringing reef off one of the Palm 

 Islands, in which the coral may be recognised, forming thick bush-like clumps immediately 

 beneath the surface of the water. Some few additional species of the genus Millepora have 

 been obtained from the Barrier district ; none of them, however, appear to construct coralla of 

 substantial size, and they for the most part form simply nodular or encrusting masses. 



The coralla of the Millepores may be readily distinguished from those of the typical Madre- 

 pores by the character of the "polyp cells." Instead of taking the form of definite corallites sub- 

 divided by symmetrically radiating septa, these "cells" are represented by simple circular 

 perforations, most commonly forming distinct groups, in which one slightly larger perforation 

 occupies a central position, and has distributed around it, at uneven distances, some four or five 

 smaller pores. The true nature and affinities of the Milleporids were first pointed out, many 

 years since, by the American naturalist, Alexander Agassiz; but it remained for Professor H. N. 

 Moseley, in association with the scientific expedition of H.M.S. Challenger, to elucidate thorough!}' 

 the full details of their structure ; and upon his important monograph on the subject the illus- 

 tration of the polyps of Millepora alcicornis, given in Chromo plate VI., Figs. 8b and c, have been 

 based. A small portion of the corallum is also shown in its natural size and colour in Fig. 8 

 of the same plate. As with the anomalous Alcyonoid coral, Hdiopora canilca, described on a 

 previous page, the polyps of Millepora appear to be exceedingly shy of expanding when in 

 captivity. During none of the short intervals in which living coralla of Millepora were under 

 the author's observation, was the much-looked-for expansion of the polyps observed. 



There is another genus of the class Hydrozoa, in addition to Millepora, which 

 secretes a dense calcareous corallum, and contributes its share, in death if not in life, towards 

 the building up of the Great Barrier edifice. This is the Distichopora coccinea, represented 

 by Figs. 6 and 6a of Plate XI. of the coloured series. The most conspicuous feature of this 

 type is its brilliant vermilion red or crimson hue, combined with a not inconsiderable super- 

 ficial resemblance to the precious coral of commerce, Corallinm ritbrmn. On nearer examina- 

 tion, however, it is found to differ so fundamentally in its minute structure, that it is valueless 

 tor commercial purposes. In addition to the larger perforations, resembling those of its near 



