BY G. I. PLAYFAIR. 539 



Pediastrum Boryanum (Tuip.) Menegh. (Pl.lvii., f.32). 

 Forma; coenobium e cellulis 4 exstructuiii. Ccenob. diam. 40/x. 

 Botany (15). 



Var. Haynaldii (Istv.) mihi. (PI. Ivii., f.33). 



Coenobium long. 180, lat. 155; cell. diam. 32//. 



Botanic Gardens (3). 



P. n<iynaldi% Istvanffi, Jel. Magyar. Alg., 1888, p. 252, T. ii., 

 f. 38. Syn., P. angidosum v. araneosum Rac, Gatunki rodz. 

 Pediastrum, 1889, p. 18, T. ii., £40. This form is characteri.sed 

 by the fine ridging on the cell- wall. There is no difference 

 between Racil)orski's form and that of Istvantii, save that in the 

 latter the lines on the cell are granulate. 



Var. AUSTRALE, n.var. (Pl.lvii., f.31). 



Cellula3 perimetri cornibus pleiumque brevibus: incisuris altis, 

 oblongis, intus rotundatis, lateribus parallelis. 



Ccenob. long. 116-150, lat. 1 00-127; diam. cell. 12-20//. 



Botanic Gardens (3). 



A form of P. Bori/anum common and widespread here, but 

 apparently not so elsewhere. It is characterised bv the shape 

 of the marginal incisions, which are in the form of the letter U, 

 oblong with rounded ends and parallel sides. Tlie horns are 

 generally short. The margin between the horns of the two 

 adjacent cells is very slightly concave. 



Pediastrum biradiatum var. Braunii (VVarim.) (Jhud. 



Cell. long. 24, lat. 12/x. Kyogle(219). (PL Ivii., f.35). 



C/'. Chodat, Alg. vertes, p. 230. >Syn., P. Praionii' Wiirlnrdiun, 

 8chw. Crypt. No. 32."^ P. rotula Ehr., {no7i Nageli) in A. Braun, 

 Alg. unicell., T. vi., figs. 2, 5, 6. The dimensions of the peripheral 

 cells of Braun's fig. 5 work out at long. 22, lat. 13/x. P. biradi- 

 atum Meyen, is extremely rare; 1 have never come across the 

 type, and only one specimen of the variation. The lobules of 

 the cells are bifid in this form, only incised in the type. 



^ Not having seen Waitniann's t3'pe, I .siniplj^ follow Chodat in the 

 .synonymy. Latter] lei in, however, Veg. siissw. plankt. Biiren-Insel, p. 10, 

 and Borge, Algentl. v. Schweden, p. 00, identify' it with P. trirormifum 

 Boriie. 



