OVSTERS AND OYSTER FISHERIES OF QUEENSIAND 247 



which, notwithstanding its excellent edible qualities, has (as in the case of the preceding type) 

 hitherto prevented it from occupying a prominent place in the Australian markets beside the more 

 familiar commercial varieties, is the tenacity and extensiveness of its base of attachment to its 

 rock support, which is almost invariably coincident with the entire external superficies of the 

 adherent shell. As a necessary consequence, much labour is requisite to separate the oysters 

 from their attachments; and in the operation they are so liable to injury that, if packed at once in 

 bulk and transported to long distances, a large percentage die, and engender a rapid mortality among 

 the survivors. The species is, nevertheless, brought into some of the coast towns, such as Rock- 

 hampton and Gladstone, and there realises a price corresponding with that of the ordinary commer- 

 cial form. Treated in the manner previously described for Ostrea nigro-niargiiiata (viz., laid down 

 for awhile to recover condition), it would prove equally eligible for further transport. It is a 

 question, however, whether this Ostrea mordax might not be turned to more profitable account 

 by its collection and conservation, either by tinning or otherwise, at temporarily-established sta- 

 tions in the immediate vicinity of its most abundant development. 



In dimensions, the coral-rock oyster rarely exceeds a length of three inches, and the lower 

 or concave shells in the finest examples examined possessed a holding capacity of one and a-half 

 fluid ounces. The reproductive phenomena of the species have been found by the author to 

 be essentially identical with those hereafter described for the ordinary commercial species, Ostrea 

 glomerata, there being no incubation of the brood within the mantle cavity, as in the European, 

 and the more southern Australian so-called mud-oyster, Ostrea edidis. 



The author's attention was first directed by Captain Sykes, the harbour-master of Rock- 

 hampton, to an exceedingly remarkable variety of oyster, which in some respects resembles Ostrea 

 mordax, and occurs on Rocky Island, off Keppel Bay. It is illustrated by Figs. 3 and 4 of Chromo 

 plate XIV. In this creature the hollow, beak-like, prolongation, or umbo, of the attached 

 shell, alluded to in connection with the variety cucullata, and depicted in Fig. 2 of the same 

 plate, is so abnormally developed that the movable, or opercular, valve, presents the aspect of a 

 small hinged lid set upon the summit of an elongate, corrugated tube. In the upper of the two 

 examples figured, the relative dimensions of the two shells are so disproportionate that while the 

 right, or opercular, one measures just over an inch in diameter, the left or attached one measures, 

 from its free edge to its base, no less than six inches. This extraordinary modification is apparently 

 brought about through the oysters being crowded close together on the sides of perpendicular 

 rocks, with no room for lateral expansion, growth being, in consequence, centred in the vertical 

 elongation of the attached valve. As shown by making rough sections, the cavity occupied 

 by the living oyster, in this species, extends through the anterior third only of the entire shell, 

 the remaining or basal two-thirds, consisting of consecutive chambers bounded by cellular laminae 

 that represent its successive growth-lines. 



With respect to the shape and proportions of its component shells, this tubular oyster bears 



