12 F. EK. FRITSCH. 
PLEUROCOCCACE. 
Genus PLEuRococcus Menegh. 
7. PLEUROCOCCUS FRIGIDUS. 
(Pl. L, figs. 43, 44.) 
Pleurococcus frigidus W. and G. 8. West, op. cit., p. 276, Pl. XXIV., figs. 40-44. 
Diam. cell. = 20-22 p. 
Hab.—Freshwater pond among eskers four miles north of Black Island, upon ice, 
McMurdo Strait, September 12th, 1902; Gap pond, Winter Harbour, February 20th, 
1904. 
This form was rare and was always found attached to the Phormidiwm-sheets. 
8. PLEUROCOCCUS ANTARCTICUS. 
(Pl. L, figs. 26-35.) 
Pleurococcus antarcticus W. and G. 8. West, op. cit., pp. 276-277, Pl. XXIV., figs. 49-51. 
Ilab.-—Very widely distributed on the Phormidium-sheets, especially Gap pond, 
Winter Harbour, ponds in eskers near Black and Brown Islands, ete. 
This is a very striking and characteristic constituent of the epiphytic vegetation 
of the abundant Phormidium-sheets, but obviously much more variable than Messrs. W. 
and G. 8. West’s material would lead one to suppose. According to their diagnosis the 
characteristic features of the species are: the large spherical cells, which are isolated or 
aggregated in small families; the thick cell-wall, which is homogeneous or obscurely 
stratified ; a large, indistinctly limited, parietal chloroplast ; the frequent presence of 
drops of oil. The form, they observed, was free-floating, but they also distinguish a 
forma robusta (op. cit., p. 276, Pl. XXIV., figs. 52-54), which grows on the surface of 
the Cyanophyceous strata; this form has huge cells with a very thick, stratified 
membrane and is stated to lack drops of oil. 
I have observed no free-floating specimens of P. antarcticus at all, probably 
because my Antarctic material was mainly such as had grown attached to some 
substratum. ‘There occurred, however, on some of the Phormidium-sheets groups of 
cells agreeing in all respects (except in the attached habit) with Messrs. West’s 
description (f. simplex, cf. below). These cells varied in diameter between 18 and 35 p, 
the commonest dimension being 20 »; they contained no pyrenoid, but often numerous 
starch-grains ; and globules of oil varying in size and number were often present 
between the thick walls and the contracted contents (PI. L, figs. 30, 31). 
In other groups of cells, however, one (rarely two) pyrenoids were conspicuous 
after staining with iodine, these cells otherwise agreeing in all respects with those just 
described (Pl. I., fig. 32, f. typiea, cf. below). In other groups of cells again (PI. [., 
