250 THE NATURALIST IN AUSTRALIA. 



of both these forms of oyster growth are characteristically represented in Plate XXXIX. 

 of the author's " Barrier " book. 



The most notable example hitherto recorded of oysters growing upon trees is 

 probably afforded by that delineated in the illustrations on page 249. These portray a 

 new and remarkably minute species of oyster discovered by the writer in the estuary of 

 the Ord River, Cambridge Gulf, Western Australia, when accompanying, as a guest, the 

 surveying cruise of H.M.S. "Myrmidon," in the year 1888. With reference to its re- 

 corded habitat, the name of Ostrcea ordensis was conferred upon this species in a paper 

 entitled " Oysters and Oyster Culture in Australasia," contributed by the writer to the 

 Auckland, New Zealand, meeting, 1891, of the Australian Association for the Advance- 

 ment of Science. Ostrcea ordensis grows not only on the roots, stems, and respiratory 

 shoots, or "cobbler's pegs," of the White Mangrove, Avicennia officinalis, but also on its 

 leaves. As shown, in fact, in the photographic figures reproducing the specimens their 

 exact natural size, as many as forty or fifty individual oysters may be crowded together 

 on a single leaf, measuring about two inches in length. That these oysters had attained 

 to a state of maturity was established by the fact that, on being opened, they were 

 found to be crowded with well-developed embryos. The growth zone of these oysters 

 was, moreover, considerably nearer high-tide mark than that affected by the only other 

 type, a stunted race of Ostrcea glomerata, which grew sparingly on the rocks at a lower 

 level in the near vicinity. It happens, as a consequence of their inhabiting this high- 

 level growth area, that these oysters are covered by the tide for a few hours only 

 during the course of the day. During neaps, indeed, they may be left uncovered for 

 several consecutive days. There is a famous oyster, celebrated in song, accredited 

 with a penchant for walking upstairs. The particular variety here figured has, at any 

 rate, manifested the predilection to climb higher up a tree than any oyster species 

 previously described. 



A companion picture to the "Rhinoceros Rock" heading to this Chapter has 

 been selected for its tail-piece. The rock scene in this instance portrays a somewhat 

 remarkable sandstone formation on the foreshore of Sweer's Island, a member of the 

 Wellesley group, in the Gulf of Carpentaria. The anomalous nature of this rock 

 formation is recorded in Dr. Fitton's Geological Appendix to Captain King's " Survey 

 of the Coasts of Australia," Vol. II., 1826, and is briefly referred to on page 570, 

 in the following words : " In Sweer's Island, a hill of about fifty or sixty feet in 

 height was covered with a sandy calcareous stone, having the appearance of 

 concretions, rising irregularly about a foot above the general surface without any 



