6o ■ THE GREAT BARRIER REEF. 



complete process of pearl manufacture." Betwixt this and then lies the " iiiibckniintc Zitknnft" 

 and an epoch of painstaking work. 



PLATE XXXIX. 



MANGROVE OYSTERS, KEPPEL BAY, AND THE ENDEAVOUR RIVER, 



The two illustrations contained in this plate, representative of what are known in the 

 Australian colonies as mangrove oysters, indicate two widely distinct conditions of oyster- 

 growth. The upper of the two pictures delineates a mangrove oyster-bank, visited and 

 photographed by the author, in Keppel Bay, near Rockhampton, ofT the estuary of the Fitzroy 

 River. In this instance the oysters started growth attached to the upright shoots, or so-called 

 "Cobbler's Pegs," that spring vertically from the laterally extending roots of the White Mangrove, 

 Aricennia officinalis. Around these adventitious supports the oysters have accumulated to such 

 an extent as to form an almost solid bank, between two and three feet thick. The species of oyster 

 that forms these dense aggregations is the ordinary commercial rock-oyster of Queensland and 

 New South Wales, Ostrca glonicrafa, which occurs, in a great variety of forms, from a little south 

 of the New South Wales and Victorian border, throughout Queensland, to the shores of the 

 northern territory. Within the limits of the tropics, and necessarily that oyster-producing area 

 which coincides with the boundaries of the Great Barrier Reef, this oyster is of considerably 

 smaller dimensions than in the southern latitudes where it is most extensively cultivated. 

 The oysters of which the Keppel Bay masses in the illustration are composed rarely exceed 

 two inches in their longest diameter; many being required to satisfy a healthy appetite. 

 These small-sized oysters are now transported in considerable quantities to the southern, 

 Moreton Bay, beds. Spread out with abundance of room to grow and fatten, they begin 

 to grow within a few months, and are in a year or two indistinguishable from the finest 

 Moreton Bay natives. 



In the second figure of Plate XXXIX. this same species of oyster, Ostrca glotnerata, is 

 growing in profusion on the lower moieties of the widely-spreading aerial roots of the orange 

 mangrove, Rhizophora mucronata. It was in association with oysters first observed under these 

 conditions that the reports concerning oysters growing upon trees, which for a long while were 

 regarded with suspicion as mere travellers' exaggerations, originated. It has been the author's 

 good fortune to meet, in the northern territory of Western Australia, with a species of oyster 

 which invades the mangroves to a much higher plane, being found not only on the roots and 

 stems, but also on the growing leaves of the mangrove bushes. This oyster is apparently the 

 smallest known. Its shells rarely exceed one quarter of an inch in length, and are so minute 

 that fifty full-grown individuals have been counted on a mangrove leaf two inches long. With 



