2 50 THE GREAT BARRIER REEF. 



Although an oyster identical with the so-called mud-oyster, Ostrea ediilis, of the more 

 southern colonies has not been obtained from Queensland waters, a species bearing some resem- 

 blance to it has been sparingly captured by the author, with the aid of the dredge, in Moreton Bay, 

 and in considerable abundance from Cleveland Bay and other northern districts, where it is 

 utilised as food. A highly characteristic feature of this species is the single large indentation of 

 its free border, which gives to its otherwise sub-orbicular shells a saddle-shaped contour. It 

 has also a peculiarly thickened margin, the outer edge of which, when fresh from the sea, is 

 coloured a delicate rose-pink. A figure, representing a profile view of the conjoined shells 

 of this oyster, showing their characteristic curvature, is given in Chromo plate XIV., Fig. 6. 

 It not having been found possible to identify this mollusc with any of the species hitherto in- 

 cluded in the Australian list, it is here proposed to provisionally associate with it the title of the 

 Saddle Oyster — Ostrea sellaformis. The largest specimens so far observed, measured as much as 

 four or five inches in diameter, a size calculated to yield a substantial amount of "meat." 



A species of bivalve classed among oysters in popular terminology, but which belongs to the 

 genus Spondylus, demands brief attention, with reference to the fact that it is very unwholesome 

 eating, if not absolutely poisonous. While occurring as far south as Moreton Bay, it is most 

 abundant among the coral-reefs of the tropical coast-line. It may be easily recognised by the 

 symmetrical ovate shape and convexity of its component shells (the lower or attached valve 

 being particularly deep and cup-like), and also by the peculiar formation of the hinge-joint. 

 The shelly teeth of this structure so interlock with one another that, while the valves open 

 and close with the greatest readiness, they cannot be separated from one another without 

 force, even after the death of the animal and the disintegration of their connecting ligament. 

 The "flesh" of this false oyster when opened is of a pale pinkish hue. If partaken of 

 in any quantity, in mistake for some ordinary edible variet}', severe purging and nausea 

 usually ensue. 



THE ORDINARY COMMERCIAL OYSTER, OSTREA GLOMERATA—\T?> 



INDIVIDUAL MODIFICATIONS. 



The ordinary commercial oyster of Queensland, with which the appellation of the " Rock 

 Oyster " is most popularly associated, is best known, scientifically, as the Ostrea glomerata of 

 Gould. This bivalve, however, is subject to such an infinity of individual variations, dependent 

 upon its special conditions of growth and environment, that some conchologists have been led 

 to confer a separate specific name upon each most prominent variety. Since, however, there 

 abound intermediate modifications which unite these, at first sight divergent, types into one 

 harmonious series, the latest scientific opinion is in favour of including the whole within the 

 single specific title above cited. 



