502 \EW AND RARE FRESHWATER ALGiE, 



this genus; and the sheath, though very delicate, was quite dis- 

 tinct in broken filaments. I have always found it so, even in 

 the finest species of Oscillatoria. The filaments, in general quite 

 straight, were bent suddenly about 10// from the end, which was 

 not attenuated. 



Oscillatoria simplicissima v. granulata, n.var. (PL liv., f.2). 



Forma dissepimentis tenuissime granulatis. 



Diam. fil. 8, cell. alt. 4-6 (plerumque 4/i,). 



Lismore (327). 



Filaments free-floating in prodigious quantities, colour pale 

 grey-green, contents finely granular, as also are the dissepiments. 



Var. CONSTRICTA, n.var. (PI. liv., f.3). 



Forma trichomatis ad genicula levissime constrictis. 



Diam. fil. 13, cell. alt. 4-8/x. Lismore (350). 



Filaments free-floating, more than half as bi'oad again as in 

 the type, with the cells slightly constricted, a mere nick at the 

 edge. Colour pale blue, contents homogeneous not granular. 

 Type in Gomont, Monog. d. Oscillariees, p. 2 19, PL vii., f.l. 



Oscillatoria princeps Vauch. (PL liv., f.4). 



Diam. fil. 30-57, cell. alt. 4-8/x. Lismore (350, 352). 



Colour pale grey-blue or grey-green. I mention this species 

 for the sake of giving a figure of a piece of empty sheath show- 

 ing fixed dissepiments right across, with incipient intermediate 

 ones. In surf ace- view, the septa appeared as faint transverse 

 lines, but, in optical section, they showed bulging to one end, as 

 if the cells had been violently forced out. 



Genus P h o r m i d i u m Kiitz. 



Phormidium GRANDE, n.sp. (PL liv., f.5). 



Stratum papyraceum olivaceum; fills rectis, apicibus rotundatis, 

 calyptra nulla, vaginis plerumque crassis; trichomatis saturate 

 viridibus interdum luteolo-viridibus, ad genicula baud constrictis; 

 articulis brevissimis; dissepimentis latis, baud granulatis; cyto- 

 plasmate tenui-granuloso. 



