PHOTOTYPE PLATES NOS. XVIII. AND XIX. 29 



more or less covered with a fine alluvial deposit. It has been previously remarked that 

 this species is represented in the present reef-area to the exclusion of all other coral varieties. 

 Scattered over the surface of the exposed reef, there is, at the same time, a thick sprinkling of 

 tufted algas ; while, projecting above the surface of the water in the farther pools, may be ob- 

 served the projecting tips of the broad-bladed, grass-like, Zostera, or an allied plant, which 

 constitutes the favourite food of the Dugong. 



The re-identification of the scene of this photographic view, with the included corals, can be 

 easily accomplished in association with the conspicuous landmarks. The extensive foreground 

 area represents a portion of the low foreshore at the back, or east side, of Thursday Island. 

 The high ground that constitutes the entire horizon is a part of Hammond Island, recently 

 brought into prominent notice through the discovery of conspicuous gold deposits ; and the 

 small islet in the middle distance is an ancient aboriginal burying-site, known as Dead 

 Island. 



PLATE XIX. 



ILCYONilRIM REEF, THURSDAY ISLAND, NO. 1. 



This photographic reproduction has been selected with the object, generally, of illustrating the 

 lemarkable extent to which Alcyonarian corals may fulfil the role of reef investiture, and for the 

 purpose, specially, of indicating the natural aspect in situ of that most interesting representative 

 of the order, Heliopora cceriilca. In relation to the general presentment, it may be observed that 

 there is scarcely a spot throughout the area photographed that is not occupied by an Alcyonarian 

 polypary. Close against the foreground, on the right-hand side, lies the disintegrated corallum of 

 a defunct Madrepora. These, together with the traces here and there of a basement of more 

 massive, lifeless, coral blocks, indicate that this was originally a luxuriant coral area that has been 

 invaded and gradually smothered off by the insidious Alcyonaria. 



Several specific varieties of these fleshy representatives of the coral class may be recognised 

 in this picture. The most conspicuous type is the one with large, obtusely-lobed polyparies, some- 

 what resembling elephants' feet in contour, that occupies the centre of the reef-area, and spreads 

 obliquely down towards the left. This species, which received brief notice in association with 

 Plate VIII., No. 2, is apparently identical with the Sarcophyton (Alcyonimn) glaucum of Dana. As 

 previously remarked, the polyparies vary in tint from glaucous or verdigris-green to golden- 

 yellow or brilliant lilac, and may even change their tints individually within a few days. In their 

 young, initial condition, these irregularly-lobate polyparies are, as in the illustration given in 

 Plate X. of the coloured series, simply mushroom-shaped or peltate. The innumerable polyps, what- 

 ever may be the tint of the associated polypary, are invariably bright 3'ellow in hue and mounted on 

 long, highly extensile and contractile footstalks. The second species of Alcyonium, which occupies 



