FRESHWATER ALGAi. 45 
The sheaths somewhat resemble those of N. commune. The species is also somewhat 
like NV. spheericum Vauch., but differs in the lax arrangement of the trichomes, and the 
presence of distinct sheaths. 
62. ? Nosroc SPHARICUM. 
Nostoc sphericum Vaucher, Hist. d. Conferv. d’eau douce (1803), p. 223, Tab. XVI., fig. 2; Bornet et 
Flahault, tom. cit., pp. 208-209. 
Diam. cell. veg. = 3-41; diam. heterocyst. = 5°5-6 p. 
Hab.—Freshwater pond in eskers upon ice, half-way between Black and Brown 
Islands, January 8rd, 19038. 
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 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. borneti Gain (op. cit., pp. 1691-3) is a form 
of this species. 
63. Nosroc COMMUNE, 
Nostoc commune Vauch., op. cit., p. 222, Tab. XVI., fig. 1; Bornet et Flahault, op. cit., pp. 203-207. 
Diam. trich. = 4°5-5 w; diam. heterocyst. = 6-7 p. 
fHab.—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. 
xenus ANABENA Bory. 
64. ANABAENA ANTARCTICA sp. Nn. 
(Pl. IL, figs. 118-120.) 
Filis seepe remotis, stratum definitum non formantibus, subrectis vel modice 
flexuosis, in superficie Phormidii epiphytis; vaginis arctis, seepe inconspicuis ; cellulis 
parvis globosis vel ovalibus, diametro 1—2plo longioribus ; heterocystis globosis vel 
