K)6 THE GREAT BARRIER REEF. 



contracted, do not completely disappear within the substance of the coralluni, but remain on 

 its surface in the form of minute spherular aggregations, which, in association with the abundant 

 spicular encrustment, communicate to the coralluni a rough granular, in place of a smooth leathery, 

 texture. The colony-stocks in this group, represented by the genus Spongodes and its allies, 

 usually consist of fleshy incrustations, out of which arise independent coralla, mostly of a 

 subclavate outline, with their distal extremities subdivided into short, ramifying branchlets. 

 Among the numerous species of this series that are conspicuously represented on the tidally- 

 exposed coral-reefs of the Great Barrier system, the form growing in masses to the extreme 

 left in the foreground of the reef-view, Plate III., probably occupies the most prominent position. 

 The same species is less conspicuously represented, on either side of the radiating leathery 

 type, Sarcophyion radiata, illustrated in Plate XX. The ordinary colours of the coralla of this 

 species of Spongodes are a pinkish-lilac, inclining sometimes to a bluish and in others to a 

 reddish shade of the same tint ; while the spherular polyp aggregations, usually a lighter hue 

 of the general ground colour, are not unfrequently bright golden-yellow. In contrast with 

 those of the leathery types, previously enumerated, the polyps in this genus are not, in exten- 

 sion, mounted on elongated stalks, but attached in an almost sessile manner to the lobate 

 branchlets of the corallum. Typical coloured illustrations of the corallum and polyps of this 

 genus are included in Figs, ii and 12 of Chromo plate No. X. In a second species of 

 the genus Spongodes, which not unfrequently forms considerable patches on the reefs in Torres 

 Strait, the entire corallum with the associated polyps is an opaque creamy-white. 



The genus Xenia and its allies, represent a third group of the Alcyonarian corals that 

 enters largely into the reef fauna of the Great Barrier system. Its members may be distinguisiied 

 from those of the preceding genera, by the fact that the component polyps are entirely in- 

 capable of contraction, and merely fall together into a shapeless mass on the retreat of the tide. 

 Many species of this genus, in addition to forming extensive patches on the surface of the reef, 

 hang in dripping clusters, when the tide is down, from the under sides of hollow rocks or coral 

 boulders. The polyps of all the observed members of the genus Xenia are considerably larger 

 than those of the preceding genera, their expanded tentacles not unfrequently measuring as 

 much as, or more than, an inch in diameter. These polyps, moreover, exhibit a far more exten- 

 sive range of coloration, the tints in many instances being remarkable for their delicacy. The 

 general aspect of an individual polypary of this Alcyonarian genus may be aptly compared to a 

 sheaf, having a subcylindrical consolidated base, with delicate, eight-petalled, star-shaped flowers 

 radiating in profusion from its summit. Among the more notable Barrier Reef representatives 

 of these sheaf-like forms, one species, identified b^' the author with the Xenia elongata of Dana, has 

 polyps about half-an-inch in diameter, whose tentacles are the most delicate porcelain- or electric- 

 blue, their individual stalks and the common supporting base being a somewhat browner shade of 

 the same tint. This specific type is a representative of the series in which the tentacles, instead 



