554 



EEPORT — 1891. 



indentations of its free margin. It occurs m some abundance 

 along the Great Barrier Eeef system of Northern Queensland, 

 and through Torres Straits to New Guinea. Shells of this 

 species have been obtained by me weighing no less than 61b. 

 the pair, and having a diameter of from 8iu. to lOin. At the 

 opposite end of the scale I may make mention of an exceed- 

 ingly minute species of oyster discovered by myself in the 

 estuary of the Ord Eiver, Cambridge Gulf, Western Australia, 

 in connection with the surveying cruise of H.M.S. " Myrmidon" 

 in the year 1888. This oyster, which but rarely exceeds ^in. 

 in length, is usually considerably smaller. It grows in great 

 abundance not only on the stems, roots, and respiratory shoots. 



Pigmy oysters on " cobbler's peg." 



or so-called " cobblers' pegs," of the white mangrove (Aviccnnia 

 officinalis), in the district named, but also on the leaves of the 

 same plant. The only other species of oyster that grows in 

 the same neighbourhood is the stunted tropical variety of the 

 commercial rock-oyster, Ostrca glomerata, previously referred 



to. The distinctness of the miniature species from the young 

 or spat of the last-named type was clearly manifested, not only 

 with relation to their comparative shape and size, but in their 

 respective areas of growth, the minuter form being restricted 

 to a baud of foreshore so close to high-water mark that it is 

 submerged for two or three hours only during each tide ; Ostrea 

 glovierata, in its immediate neighbourhood, on the other hand, 

 was confined to rocks that were not exposed to view until the 



