216 DR. F. E, FRITSCH ON FRESHWATER ALGÆ 
snow material and above described belong to one and the same form, as 
numerous connecting-links were observed. Rather rarely isolated cells 
of the Chlamydomonas-type were met with in the material; some of these 
certainly belong to species of Chlamydomonas (cf. below), but others may 
well be single swarmers of the Spherocystis-colonies. Occasionally one finds 
more or less rounded granular cells with a wide envelope of delicate mucilage 
around the very delicate cell-wall; these cells agree in all respects with those 
of a normal colony, and it seems very probable that such stages constitute 
the commencement of a new colony. I have, however, been unable to 
demonstrate cilia in these cells, 
The chief differences between Spherocystis Schroeteri and Glaococcus 
mucosus on the one hand and the yellow snow form on the other may be 
summarised as follows:—(1) The colonies of the latter are frequently 
rather more irregular in shape than those of the former ; (2) the cilia, if 
present, are much shorter ; (3) the cells are of somewhat smaller dimensions 
and more frequently oval in shape; (4) Schizochlamys-like stages have not 
been observed ; (5) the storage of fat. As I cannot feel certain of the 
occurrence of cilia in the yellow snow form, it will be best referred for 
the present to Splurroeystis. Sehroeteri as a forma nivalis*. It is of con- 
siderable interest that so abundant a Plankton-form as Spherocystis should 
form an important constituent of the yellow snow flora. 
(i) Tnoeniscia aNTARCTICA, F. E. Fritsch. (РІ. 10. fiv. 30. 
. ? > 
I have already referred to the abundant occurrence of species of Trochiscia 
in the Antarctic material ; one of them is characteristic for the yellow snow 
flora (PI. 10. fig. 30), although not particularly common. It consists of 
isolated spherical cells with a thiek and rather gelatinous-looking wall, which 
is uniformly covered with small processes. The latter have typically the 
shape of truncated wedges with the truncated surface outermost, so that the 
cell presents the appearance of a cogged wheel. There is, however, con- 
siderable variety in the degree of differentiation of these processes, all 
transitions having been found from cells in which the processes are but feebly 
indicated (probably young daughter-cells?) to such as have very prominent 
processes ; in the latter case they are often of slightly unequal length. The 
processes appear to be interconnected by a network of ridges. The cell- 
contents were always a little contracted ; еу appear g 
show а well-marked central pyrenoid. Starch is always present, but fat is 
rare in this form, although now and again cells were found with quite a large 
quantity of it. 
oranular and often 
This species of Trochisci appears to show some resemblance to Т, halophila 
* Cf, p. 324. 
