62 THE GREAT BARRIER REEF. 



title ol Ustira ii/on^iix, flourishes in the purest salt water, attaining its maximum development 

 on the storm-stranded coral-masses, or natural rock formations, at about half-tide mark, of 

 the reef islets and mainland foreshores throughout the Great Barrier district. The illustration 

 represents aggregations of the species encrusting rock boulders and eroded coral-stocks on the 

 foreshore of one of the Northumberland Islands group, lying some twenty miles eastwards of 

 Mackay. Conspicuous in the interstices that separate the rocky boulders from one another ma^' 

 be observed the accumulated (h'brix of Stags'-horn and other branching corals. More distinct 

 illustrations of this species, which, with relation to its most characteristic habitat, is distinguished 

 in this volume by the title of the " Coral Rock Oyster," will be found in the Chromo-lithographic 

 plate No. XIV. The remarkable variety of this species, described in a later chapter, that has 

 the attached valve de\'eloped in an elongate, camerated, fashion, after the manner of Ostrca 

 coriiiirof^itr, is illustrated in the same plate. 



PLATE XL I. 



(S.) CULTIVATED OYSTER-B]^NK, MORETON BAY. 



Both this and the succeedmg picture represent conditions of growth of the commercial species 

 of oyster, Oslira gldiiirrata, that is illustrated in the two preceding plates. This particular 

 illustration depicts one of the natural Moreton Bay oyster-banks, some little distance south of 

 the Barrier district, that is utilised for the systematic cultivation of the mollusc for the Brisbane 

 and Sydney markets. In their natural condition the oysters on this bank are attached in 

 clusters to ironstone pebbles. The bivalves grow, however, to larger dimensions, on being 

 separated and distributed in such manner that they can obtain a more abundant food supply, 

 and having sufficient space around them to allow of their fullest symmetrical enlargement. 

 As recorded in the descriptive account of the Keppel Bay oyster-reef, it is to extensive level 

 banks of this kind that the small, closely-crowded, reef and mangrove oysters from the bona 

 fuir Piarrior latitudes arc transported and successfully cultivated. 



(B,)-WHELK OYSTER-BflNK, MORETON BM. 



To the uninitiated, the oyster-bank that forms the subject of this illustration possesses no 

 special feature to distinguish it from the preceding one. A very important point of divergence, 

 however, is embodied in the fact that ironstone pebbles, or other rock formations, are 

 entirely absent, and that the thickly-associated oysters are almost universally attached to a 

 species of so-called "oyster-whelk," Poiamidcs cbernitius. In their primary condition of 

 attachment, in the form of spat, the oyster-whelks are alive, and travel freely over the surface 



