FRESHWATER ALG^E. 43 



The sheaths somewhat resemble those of N. commune. The species is also somewhat 

 like N. sphsericum Vauch., but differs in the lax arrangement of the trichomes, and the 

 presence of distinct sheaths. 



02. ? NOSTOC SPH^RICUM. 



Nostoc sphcericum Vaucher, Hist. d. C'onferv. d'eau douce (1803), p. 223, Tab. XVI., fig. 2 ; Bornet et 

 Flahault, torn, cit., pp. 208-209. 



Diam. cell. veg. = 3-4 p. ; diam. heterocyst. = 5 5-6 p. 



Ilab. Freshwater pond in eskers upon ice, half-way between Black and Brown 

 Islands, January 3rd, 1903. 



This form appeared as small colonies loosely attached to the surface of the 

 Cyanophyceous sheets, or free-floating ; the colonies were spherical or ellipsoidal (or 

 slightly irregular as a result of mutual pressure) and up to 300 p. in diameter. Some 

 of the colonies were yellowish or brownish, the colour apparently being due to the 

 general mucilage. At many points large numbers of these small (and probably 

 young) colonies were densely aggregated. The trichomes were rather loosely inter- 

 woven, the only respect in which the specimens differed from the published descriptions 

 of the species. No spores were seen. 



It seems possible that N. hornet i Gaiu (op. cit., pp. 1691-3) is a form 

 of this species. 



63. NOSTOC COMMUNE. 



Nostoc commune Vauch., op. cit., p. 222, Tab. XVI., fig. 1 ; Bornet et Flaliault, op. cit., pp. 203-207. 



Diam. trich. = 4 5-5 p ; diam. heterocyst. = 6-7 p.. 



Hob. Dry ponds, Winter Quarters, February, 1902 ; damp spots, Granite 

 Harbour, New Bay, January 20th, 1902. 



The thalli were irregularly folded, flat, membranaceous, and of a bright blue- 

 green, olive or olive-brown colour. In parts of the colonies the flexuous filaments 

 were densely aggregated. At some points pale brown sheaths were very conspicuous 

 around the individual trichomes, being more or less constricted between the cells. 

 In the bulk of the filaments the cells were nearly spherical or barrel-shaped, but at 

 some points more elliptical. The heterocysts were also in rare cases somewhat 

 elliptical in outline. Young stages were also present. 



Genus ANAB^ENA Bory. 



64. ANAB^NA ANTARCTICA sp. n. 

 (PL II., figs. 118-120.) 



Filis saepe remotis, stratum definitum non formantibus, subrectis vel modice 

 flexuosis, in superficie Phormidii epiphytis ; vaginis arctis, ssepe inconspicuis ; cellulis 

 parvis globosis vel ovalibus, diametro l-2plo longioribus ; heterocystis globosis vel 



