BY G. I. PLAYFAIR. 513 



(\)Melosira c/ranulafa. — This diatom accounts for an over- 

 whelming proportion of the total solids, being in vastly 

 greater quantities than all the rest put together. Indeed, it 

 was necessary to allow the effluent from the washing of the 

 filters to precipitate for half an hour to get rid of some of 

 the Melosira. I am at a loss to know where it all comes 

 from. Melosira graniiJata is quite rare in all the swamps 

 and marshy places round Sydney, which I have examined, 

 and it is not strikingly more common in creek-pools. 



(2)Vegetable debris. — There does not seem to be a very 

 large proportion of vegetable debris, but no quantitative 

 investigations were undertaken. 



(3)Peridinie3e. — At every season of the year, there is to be 

 found a splendid assortment of Peridiniese in relatively large 

 numbers. 



(4)Filamentous algae. — These are not well represented, nor 

 in any quantity ; but, at certain seasons, enough green matter 

 is brought down to form into gouts when the screens are 

 hosed. These consist chiefly of Spirog. porfiralix, Mougeotia 

 sp., Bvlhoch(ete sefigera, Oedogonium sp., Zygnema sp., 

 Calothrix confervicoJa, Scytonema mirnhile, Osc. nigro-viri- 

 dis, with the filamentous Desmids, Hyal. mucosa, Desm. 

 Sv)artzii, and Desm. pseudostreptonema. 



(5)Minute organisms. — When the superfiuid was poured 

 off, the lighter portions of the plankton appeared as a whitish- 

 green, flocculent deposit upon the thick tenacious slime of 

 Melosira, from which there was no difficulty in separating 

 it. On account of the richness of the material dealt with, it 

 was not necessary to use more than ordinary decantation in 

 order to secure the Rhizosolenicp and Phyfheliea. 



With regard to these two, the Phytheliece. were scarce, and 

 need to be diligently searched for ; but Bhizosolenia erievsis 

 var. morsn was in great abundance, the field of the microscope 

 being sometimes crowded with frustules. The origin of the 

 swarms of this diatom, is a mystery greater even than that 

 of the Melosira. I have never, at any time, found Hhizoso- 



