1 68 THE GREAT BARRIER REEF. 



to become thickened throughout their lengtli, and more especially' at their distal ends, where 

 they are usually excurrent, with their surfaces finely echinulate. There is also a marked proclivity 

 of the primary and a few of the adjacent septa in this type to become elevated as simple or forked 

 branchlets, above the general level of the corallum. In the two characteristics enumerated, the 

 Tridacophyllia combines, in a noteworthy manner, the diagnostic features that distinguish two 

 separate species of the same genus, recognised as new by the author some years since, when 

 engaged in the arrangement and nomenclature of the Madreporaria in the British Museum collec- 

 tion, which were described and figured by him in the Proceedings of flic Zoological Society 

 for the year 1871, under the titles (5f Tridacophyllia alcicornis and T. cchinata. In anticipation of 

 the Palm Islands type proving to be a new species, it is herewith associated with the provisional 

 title of Tridacophyllia Qnecnslandia\ 



Another exceptional Astraeacean genus, which has been obtained somewhat sparingly by the 

 author from both the northern and central Barrier districts, is that of Merulina. The t3'pical 

 Barrier Reef representative of this genus, Merulina aiiipliata, likewise forms elegant foliaceous 

 coralla, which may be of considerable extent, and are frequently developed in the form of 

 elevated crests and frills. Unlike Tridacophyllia, the polyp centres in this generic type are 

 relatively small, and are thickly distributed throughout the surface of the corallum in sinuous 

 or branching series, somewhat after the manner of those of a Meandrina or Cceloria, but on a much 

 more irregular and interrupted plan. As in Meandrina, the polyp tentacles when fully extended 

 are inconspicuous and almost transparent. The colours of the living coralla of this species are 

 usually light ; in some examples observed, a delicate cream colour predominated ; in others, 

 collected on the Palm Islands reefs, a pure pink, or light yellow, with pink septal ridges, were 

 equally mingled ; while in a third series the coralla were entirely buff, with the exception of a 

 white border to every folium or elevated frill. Coloured illustrations of this species are fur- 

 nished by Figs. 9 and 10 of Chromo plate No. VII. 



The genus Hydnophora may be said to represent a more pronounced development of the 

 peculiarities of Merulina. In this generic group the coralla are composed of either solid masses or 

 foliaceous expansions, which may be raised in the form of simple or more or less branching tufts, 

 while the septal systems are concentrated together in such manner as to form, collectively, minute 

 conical elevations that are distributed evenly throughout the surface of the corallum. In one 

 species, apparently identical with the Hydnophora rigida, collected by the author at the Palm 

 Islands, delineated in Fig. 8 of Chromo plate No. VII., the corallum assumes an erect branching 

 character resembling that of an ordinary Stags'-horn coral, Madrepora, for which, indeed, it was 

 at first sight mistaken. The record of this species as a Great Barrier type is of interest, since, 

 from the time of its earliest discovery by Dana, in the Fijis, it has been lost sight of, and has 

 occupied an uncertain position in the classificatory systems of Milne Edwards and other 

 zoophytologists. There are circumstances associated with the structure of the polyps and their 



