248 



THE NATURALIST IN AUSTRALIA. 



is to be seen above it, and they are very thinly scattered beneath its abruptly 

 defined lower edge. The depth of this veritable oyster girdle is about eighteen 

 inches, and it projects from the surface of the rock to a thickness of over one foot. 



This and other photographs illustrative of this remarkable 

 growth condition were taken by the writer in the vicinity of 

 Eocky Island, off Cooktown, Queensland, one of the many 

 granitic island formations that are hereabouts intercallated 

 among the Great Barrier system. 



The popular title of the Coral Eock Oyster has been 

 given by the writer to Ostrcea mordax with reference to the 

 fact that it occurs in great abundance and to the exclusion of 

 the ordinary Eock oyster, 0. glomerata, on the outlying rocks 

 and reefs of purely coral origin throughout the tropical Aus- 

 tralian coast-line. A very singular modification of this oyster 

 species is represented in the adjoining process-prints. Through 

 growing in crowded juxtaposition much after the manner shown 

 in Plate XLIIL, the lower or attached shell elongates in- 

 definitely, while the outer or opercular one retains its normal 

 dimensions. The originals of these illustrations, which are re- 

 produced life-size, were obtained in the neighbourhood of 

 Keppel Bay, Queensland. A very closely corresponding variety 

 of the ordinary Eock Oyster, 0. glomerata, produced under 

 parallel conditions, has been more recently obtained by the 

 writer at Shark's Bay in Western Australia. 



Australia is, par excellence, to the unsophisticated 

 Britisher, the land of incongruities and topsy - turvydom. 

 Christmastide is a mid-summer festival ; the swans are black ; 



CORNUCOPIA-LIKE VARIETY OF OSTR^EA MORDAX. KEPPEL BAY, QUEENSLAND. NATURAL SIZE. 



