CORALS AND CORAL-ANIMALS. 169 



relationship to the conical elevations of the substance of the corallum in this species, and in 

 another obtained from the Barrier district, that may render its relegation to a separate genus 

 desirable. In both this and the second form referred to, the oral apertures of the living polyps 

 are distinctly associated with the summits of the conical elevations, and the surrounding tentacles 

 are very distinctly capitate. In Hydnophora microcona and H. Dcmidojfi, on the other hand, the oral 

 apertures occupy the centres of the depressions betwixt the elevated cones, and the tentacles are 

 subulate and very attenuate, communicating to the living corallum, when the polyps are fully 

 extended, an almost hirsute appearance. The differences indicated will be readily apprehended by 

 a reference to the Figs. 7, 8, and 13 of the Chromo plate No. VII., illustrative of this genus. 

 Should a separate generic title be required for the distinction of the capitate-tentacled species, 

 the one of Monticulina, formerly conferred by Lamarck on certain members of this generic group, 

 might be appropriately revived. 



Respecting the life colours of the Hydnophoras, there is some little latitude of variation. In 

 H. iiiicrocoiia, Chromo VII., Fig. 12, obtained from the Mid-Barrier Reef, near Adolphus Island, 

 Ten-res Strait, in which the corallum forms massive undulating hillocks, the general ground 

 colour, and that of the polyp tentacles, is brilliant grass-green, and the conical septal elevations 

 are light brown. In another form, H. Demidoffi, from the same district, in which the coralla 

 beginning as an irregular encrustment, are subsequently elevated into crests, cones, and ridges 

 of divers fantastic shapes, the ground colour is a pale chrysoprase, or jade-green, and the septal 

 elevations and polyp tentacles are light brown. In the arborescent Palm Islands type, H. rigida, 

 first described, the ground colour is creamy-white, and the distinctly capitate tentacles are either 

 pale lemon-yellow or the lightest emerald-green. 



The exceptional, arborescent, species of Hydnophora last referred to, prepares the way 

 for the consideration of that series of the aporous Madreporaria, in which an arborescent or 

 more or less branching t3'pe of structure represents the normal growth. One family, that of 

 the Oculinidas, most abundantly developed in the West Indian coral seas, but rarely occurring 

 among the Great Barrier reefs, forms erect branching coralla, whose shrub-like aggregations 

 may be two feet or more in diameter. The substance of the corallum in the typical members 

 of this family is remarkable for its pure whiteness and great density ; and, but for the almost 

 obliterated perforations through it, that represent the polyp centres, it would take a high polish, 

 and might be turned to profitable account for the manufacture of articles of jewellery. It is remark- 

 able that only a single representative of this group, in some respects resembling Ociiliua Pctivcri, 

 but apparently a new species of the genus, was personally obtained by the author, and this one 

 was peculiar to the locality of the Barrier district. The type in question grows in some abundance, 

 and is just accessible by wading, at lowest spring-tides, on the fringing reef of one of the Palm 

 Islands series, known as Orpheus Island. The coralla of this Oculina, as they grow /;; situ, are 

 very attractive objects, forming dense bushes of considerable dimensions, the general ground 



