48 C. HEDLEY. 



The solid shell it carries is armour proof against the jaws 

 of fish, the beaks of gulls, or the teeth of rats, and the rays 

 of the sun. Both crab and snail live on the bare ground. 

 Though no food is visible it may be that each tide in a 

 layer of silt spreads a table of microscopic provender. 

 The zones of Melaraphe and of Donax share this feature 

 of exhibiting no apparent vegetation. In the tropics this 

 zone carries a larger fauna and includes the amphibious fish 

 Periopthalmus, and the brightly coloured calling-crab, 

 Ilea, and the gasteropod Telescopium. 



Along the calm and sheltered reaches of Botany Bay, 

 Port Jackson, or Broken Bay, there flourish marine meadows 

 of Zostera, Posidonia, and like plants with ribbon blades, 

 known as grass-wrack or eel grass. The commonest species 

 is Zostera nana 1 (fig. 13). These species flower here only 

 on very rare occasions ; during the last twenty-five years 

 I have found Posidonia in blossom only once and never 

 Zostera, Their dense foliage smothers any intruders, so 

 that they occur almost as a pure formation. Such an 

 association is termed a zosteretum 2 (Plate II, fig. 3). 



Under the microscope, the leaf blades of the Zostera 

 develop into a zoological garden, so overgrown are they 

 with minute plants and animals. The fauna of the Zostera 

 beds near Marseilles was described by Prof. Marion. 3 Dr. 

 H. 0. Ostenfeld has produced an exhaustive memoir on the 

 Ecology of Zostera in Danish waters. 4 He finds it to sup- 

 port an epiphytic flora of small sea- weeds and diatoms and 

 a fauna of small gasteropods and bryozoa. There it is the 

 principal source of the organic matter of the sea bottom. 



1 This and the Ruppia were kindly identified for me by Mr. J.H. Maiden. 



2 Warming, (Ecology of Plants, 1909, p. 230. 



3 Marion, Ann. Mus. Marseille, i, 1883, p. 71. 



4 On the Ecology and Distribution of the Grass- wrack, Zostera marina, 

 in Danish waters. Report Danish Biological Station, xvi, 1908. See also 

 Petersen, Reports xx, 1911, and xxi, 1913. 



