536 NKW ANr) RAKR FRESHWATER ALC.X,. 



Tetraedron minimum V. RECTiLixEARE Plavf. (PI. Ivii., f.25). 

 Cell. long. 11 J, lat. lOJ/x. Botanic Gardens, Sydney (3). 



Cf. Australian Freshwater Phytoplankton, these Proceedings, 

 1917, p. 842, PI. 58, f.l6, 17. Known to me previously only from 

 Guildford. A rare form. 



Tetraedron obtusum, n.sp. (PL Ivii., £.26). 



Cellulas tetraedricai: lateribus rectis; angulis rostratis; rostris 

 crassis quadratis, brevibus; apicibus truncatis. 



Cell. diam. 21/x. Lismore (362). 



Cell tetrahedral, sides straight, angles produced into a siiuV^ 

 nosed rostrum, the latter broad, quadrate, truncate. 



Tetraedron trigonum Nag., forma (PI. Ivii., f.27, 28;. 



Forma lateribus in medio quam levissime retusis; spinis bre- 

 vissimis oblique recurvis; membrana crassa. 



Cell. diam. 36, crass. 20/x. Lismore (345). 



Svn., Polycdrium tetragonum f3 piinctatum (Kirchn.) Lag., 

 Bidrag till Sveriges Algflora, p. 62, T. i., f.28. P. trigonum e 

 pu7ictatum Kirchii., Alg. v. Schles., p. 104 (sec. Lagerheim, I.e.). 

 The type has sides simply arched, with or without a small 

 straight spine at the angles. In this form, the sides are slightly 

 flattened or retuse in the middle, and the spines are obliquely 

 recurved. Our specimen was not punctate. For the type, cf. 

 Nageli, Gatt. einz Alg., T. iv.B, figs-ln- and 3«, b only. 



Fam. HYDRODICTYACE/E. 

 Genus P e d i a s t r u m Meyen. 

 Pediastrum simplkx Meyen. (PI. Ivii., f.29, 30). 

 Ccenob. (cell. 4) c. proc. long. 35-50, lat. 33-48; s. proc. long. 

 17-24, lat. 16-22; cell. long. 24-34, lat. 12-17/x. Ca?nob. (cell. 8) 

 diam. 50-64; cell. long. 18-24, lat. 8-1 2/x. 

 Parramatta Park (99, 136). 



Meyen, Beob. ub einig. nied. Algenf.,( 1829) T.xHii., f.l. 8yn., 

 P. simplex var. radians Lemra., Zeitschrift f. Fischerei, 1897; P. 

 s im])le.i: fS aiinulatum Choda^t, Alg. vertes, p.225, 1902; P. simplex 

 V. clathratum f. radians (Lemm.) G. J-^. West, Third Tanganyika 

 Exp., p.l34, 1907. 



