10 



of 10s. per 1000 rendered them cheaper for the purpose than any article previously employed. With 

 attached wire handles they were more convenient for handling on the exposed banks, and could, in addi- 

 tion, be easily deposited in or raised from water of a fatliom's depth. Their individually larger superficial 

 area entailed a considerable saving of labour iu their manipulation, while, as indicated on a preceding 

 page, the circumstance of the cemented .surface being raised by the attached bricks or stones some few 

 inches off the ground secured to the young oysters an iraraunity from the attacks of crabs, whelks, star 

 fishes, and other enemies to which they are exposed when the cemented surface, as is the case of tiles, is 

 in immediate contact with the ground. 



The " split paling " type of spat collection, as figured iu Plate VIII., is, in my opinion, after an 

 experience of its successful employment under a variety of conditions, the most convenient and economic 

 form to employ in Australian waters, and may be characterised as an essentially Australian product. 

 Sawn boards may, as a matter of course, be fashioned into collectors of identical form and efficiency, 

 but at many times their cost, the relative price of the respective materials averaging 20 feet for Id. 

 for the split palings, and l^d. per foot for the sawn wood. In practical use the split palings are further 

 found to possess an advantage over the sawn material, through the roughlv ]iarted natural grain of the 

 wood furnishing a more favourable key for the attachment of the cement. When split to order for this 

 purpose they should average at least an inch in thickness, and have as rough a surface as it is possible to 

 obtain. "Where split palings are not procurable the rough discarded rails or boarding of any description 

 that is usually abundant around ever)- settlement, may be pressed into service and be made to do good duty 

 before final condemnation for firewood. In the preparation of these collectors the palings or boards 

 should be soaked for a day or so iu the water in order that the grain may swell to its full extent before 

 the application of the ceinent. Should this precaution be neglected the cement will not adhere to the 

 wood. Salt water is as good as fresh for mixing the cement, and, as the process may be most con- 

 veniently performed at the water's edge in the immediate neighbourhood of the beds under cultivation, 

 this proves a distinct advantage. From experience gained by the use of these collectors in Queensland 

 waters it may be observed that about half-tide mark represents the zone within which the most abundant 

 harvest of spat can be gathered, and that at all times of the year, though the months of February and 

 August are more especially propitious for its collection. 



On their first attachment to the cemented collectors it will be found that the young oysters adhere 

 to the cement by the entire surface of the attached shell, a condition of growth which obtains for the 

 most part in the central figure of the lower group of collectors figured at Plate VIII. After attaining to 

 about one-half of an inch in diameter, the free edges of the shells commence to grow outwards, and this 

 direction of their growth is continued until at an age of about six months they project an inch and 

 a-half or 2 inches from the collector. At this stage the young oysters may be easily detached with or 

 without the cement, and be laid on the banks as ordinary " cultivation." The collectors may then be re- 

 cemented and re-laid for the catchment of a second crop. Cemented slates have also been found by me 

 to prove very efficacious spat collectors, and most nearly approach the French tiles. Slates procured as 

 an ordinary market article are too expensive for general employment. It sometimes happens, however, 

 as occurred with the supply experimented with, that condemned lots may be obtained at but a little over 

 the cost of carriage direct from the quarries. In utilising slates for this purpose I have found it most 

 convenient for manipulation to use them in combined series, wiring sets of half a dozen or so to each 

 side of a ridge-shaped frame constructed of light saplings cut to 4 or 5 feet lengths. 



DESTRUCTIVE AGENCIES AND DISEASES. 



Among the enemies from whose attacks the Queensland oyster-grower suffers serious loss of 

 stock, the small boring whelk, Urosalpiiix paivie of Crosse, must be awarded a prominent position. The 

 destructive influences exerted by this mollusc are parallel to those of Murex tarentinus and Nassa 

 reticulata on the European oyster beds. The shell of the Queensland borer is much like that of the 

 last-named European species, but is more slender, and it has a di.stinct violet-coloured lining to the mouth 

 aperture. A figure of the species is given at Plate I., Figs. 10 and 11. The young oyster brood, from its 

 earliest attached condition up to about one-half of its adult growth, is much subject to the ravages of this 

 foe. Not unfrequcntly, it is so abundant and predaceous that almost the entire brood stock on a bank 

 or from dredgings I have investigated was found to be destroyed by this borer. Mature oysters, even, are 

 not exempt from the attacks of this enemy, one of the shells in the typical cluster illustrated by Plate I., 

 Fig. 1, exhibiting at "a" the symmetrically circular hole by which the Wrosilpinx has gained access to its 

 prey. The drilling operation is performed by these boring molluscs with the aid of a toothed ribbon, 

 technically known as the " Odontophore ", which is enclosed within, but can be partly protruded from, 

 the buccal cavity. It has been ascertained by direct experiment in connection with the European species, 

 Murex tarentinus, that the mollusc takes about half an hour to pierce the shell of a young oyster 

 one month old, and eight hours to perforate a matured one of three years' growth. The only 

 practical remedy for this destructive pest so far employed is hand-picking, a tedious process which, 

 however, can be carried into practice with considerable success on the banks, especially with the aid of 

 children, who soon become great adepts in detecting and collecting the unwelcome intruder. By these 

 means the borer has already been fairly exterminated in certain of the most carefully-cultivated banks. 

 This same species of boring whelk has been observed by me in abundance on the oyster banks aa far 

 north as Rodd Harbour and Seven-mile Creek, and where also it takes a heavy toll on the growing brood. 

 The interesting discovery was recently made and communicated to me by Mr. E. Kelk, of Brisbane, that 

 another gasteropodous mollusc, Tfatica plumlea, preys upon the Urosalpinx. This species, fir^ured at 

 Plate III., Figs 3 and 4, is of larger size than the borer, with a smooth snail-like shell. In the living 

 state a large fold of flesh, technically termed the mantle, is protruded from the shell and forms a con- 

 tinuous border of about an inch in breadth around the creature as it crawls. With tins mantle it was 

 observed by Mr. Kelk to seize and envelop the living borers and to retain them within its folds until by 

 muscular force it had dragged from its shell and devoured its victim's body. Should this recorded habit 

 of Natica plumbea prove on further investigation to be its customary one, a valuable remedy for the 

 ravages of the borer will have been discovered, and to be effected through the collection and placement 

 on the beds of quantities of Naticie to devour and keep them in check. Before the application of this 

 specific it is, however, desirable to ascertain whether or not under certain conditions, such as the scarce- 

 ness of Urosalpinx, the Naticce may not develop a latent taste for young oysters. This precaution is the 

 more necessary since in various standard natural history works small bivalve moUuscs are enumerated as 

 constituting the ordinary food of the many species of the genus Natica. Starfishes 



