248 
THE NATURALIST IN AUSTRALIA. 
is to be seen above 
defined lower edge. 
inches, and it projects 
it, and they are very thinly scattered beneath its abruptly 
The depth of this veritable oyster girdle is about eighteen 
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 
Rocky 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 Rock Oyster has been 
given by the writer to Ostrwa mordax with reference to the 
fact that it occurs in great abundance and to the exclusion of 
the ordinary Rock oyster, O. 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 XLIII., 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 Rock Oyster, O. 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 OSTRHA MORDAX. KEPPEL BAY, QUEENSLAND. NATURAL SIZE. 
