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PLANKTON OF THE SYDNEY WATER-SUPPLY. 



By G. I. Playfair. 



(Plates liii.-lvii.) 



The Sydney Water-Supply is the water of the Nepean and 

 Cataract Rivers, which is impounded in the Cataract Reser- 

 voir, and thence brought down, by many miles of canal, 

 through the Prospect Reservoir to Guildford and Pott's Hill, 

 where it is filtered by being passed through a double series 

 of wire-screens. These screens being periodically raised and 

 washed with a hose, the effluent from this operation has been 

 the principal source of material for the following notes. A 

 few samples have also been taken from the pond at Pott's 

 Hill and various tanks in the Botanic Gardens, the water of 

 which has the same origin. 



While incidentally determining the flora and fauna of the 

 plankton, one main object of this investigation has been to 

 search for the Phytheliece and Rhizosolcmu. This object has 

 happily been attained, and, although the Phytheliece were 

 not too plentiful, a very interesting series of forms has been 

 brought to light, both these and Rhizosolenia being repre- 

 sented in the plankton at all seasons. It was originally 

 intended to take a considerable number of samples, and pay 

 some attention to the fluctuations in the contents of the 

 plankton ; but, at the very outset, it was seen that the plank- 

 ton was practically constant all the year round. 



The suspended matter separated from the water by the 

 filter-screens divides naturally into five parts: (1) Melosira 

 (iranvlata, (2) Vegetable debris, (3) Peridiniese, (4) Filamen- 

 tous algae, (5^ All the lighter organisms. 



