830 AUSTRALIAN FRESHWATER PLANKTON, 



HYDRODICTYACE^. 



Genus P E D I A s T R u M Meyen. 



Pedi. tetras var. fluviatile, n.var. (PI. Ivii., f. 1). 



Cellulae sinu rectangulo, in bievem angustam fenestiaiii iiitror- 

 sum producto, miiiime incisje; angulis exterioribus apiculo minuto 

 instructis. 



Coenob. (4 cell.) long. 18, lat. 18//.. 



Lisiiiore(188). 



Instead of being deeply incised, the cells merely have the 

 outer angle excised by a more or less rectangular sinus, the point 

 of which is produced inwardly into a short loop. The free angles 

 are minutely apiculate. The markings in the cells are not 

 pyrenoids, but vacuoles in the cytoplasm; under a low magnifica- 

 tion, they appear so plainly as to be easily mistaken for a part 

 of the sinus. Cf. P. rotnla Kiltz., in Nageli, Gatt. einz. Alg., 

 T.vB, fig. 3c. 



Var. apicul\tum, n.var. (PI. Ivii., f.2). 



Cellulte extrorsum sinu amplo leviter exciste, vel alte emargin- 

 atae; angulis rotundatis, minuto hyalino apiculo instructis. 



Camob. (8 cell.) diam. 1^2; cell. diam. 7/i. 



Botanic Gardens (125). 



Syn., P. tHras var. intcf/ram (Nag.) Playf., Biol. Richm. R., 

 p. 110, PI. iii., f.26. P. intf<jrtini Nag., has the outer edge of 

 the cell quite Hat. In this form, the cells are slightly excised by 

 a wide, shallow sinus, or else deeply emarginate; the angles are 

 rounded, and furnished with a minute, hyaline apiculus. 



PROTOCOCCACE^. 



Genus Crucioenia Morren. 

 The species of Crnciijenia are, to my thinking, merely in- 

 fantile forms of Pediastrum, developed from the resting-cell or 

 zygospore, which is the outcome of the union of gametes. This 

 resting-cell, or something very near to it, I have described and 

 ficured under the name of Pedi. tetras var. unicellulare in 

 "Plankton Sydney Water-Supply," p.517, P1.56, f.I. In spite 



