BY G. I. PLAYFAIE, 



119 



of the question, as it is one of the largest forms of Oooystis, while 

 it is pretty certain (though Braun gives no note of the dimen- 

 sions) that 0. JVdgelii is one of the small plankton-forms. This 

 is sufficiently indicated by the 

 habitat: ^^ Occur rit intra massam 

 crustaceam viridem, Ahjis variis con- 

 flatam, quca truncos jnneos natatitc't 

 ohdncit,'''' and the algfe which are 

 mentioned as accompanying it, 

 while not distinctly plankton-forms, 

 are mostly such as are commonly 

 found in a free-swimming condition. 

 Moreover, 0. yiyas cannot be de- 

 scribed as ^^ species minime 7'ara" ; it is exceedingly rare. 



The only figure definitely given as 0. Ndijelii is by Kirchner, 

 Mikroskopische Welt des Siisswassers, T. ii., f.52, reproduced by 

 Chodat, Alg. vertes, p. 189, fig. 104 A (Text-fig. 106). This agrees 



Text-fig. 9. 



0. pelagica Lemm. , ( x 7oO) ; 



after Lemmermann. 



Text-fig. 10. —(rf)0. eUiptka f. mino)- W. West,(x520); after West, (b) 

 O. NcigeUi A. Br., after Kirchner. {c) Hydrocytimn macroftporum 

 Turner, ( X 375); after Turner. 



perfectly with the foregoing conclusions. Cf. PL vii., f.6, which 

 shows a mother-cell from a pond at Guildford, long. 38, lat. 23, 

 autospores 20 x 10/x, almost a facsimile of Kirchner's specimen. 

 PI. vii., f.5, is an 8-celled family from the Sydney Water-supply, 

 long. 60, lat. 48, autospores 20 x 8 ft, agreeing very well with 

 West's forms {0. elliptica, I.e.) save that the autospores are more 

 distinctly in pairs. In samples 88 and 91, free, vegetative cells 

 are abundant (PI. vii., f.1-3). 



With regard to size, West, I.e., (for 0. elliptica and f. minor) 

 gives long. 15-17, 18-21, 24-25/>i, lat. 71-8, 8-10, 11-lli/x. My 



