304 DR. Е. E. FRITSCH ON FRESHWATER ALGJE 
division ; C. antarctica, however, differs in the often appreciably smaller size 
of the cells after division, in the mucilage-sheath around the larger cells, and 
in the faculty of storing up large quantities of fat *. 
(c) ScoTIELLA ANTARCTICA, F. KE. Fritsch. (РІ. 10. figs. 7-17 ; 
Pl. 11. phots. 1, 4, 6, Sc.) 
The two species so far considered are by far the most abundant forms in 
the yellow snow flora, and the remaining members, although many of them 
not uncommon, are quite subsidiary to them. Among the latter is а very 
striking unicellular organism, which I regard as the type of а new genus, 
Scotiella T. I have observed two species of this genus, one of which 
(S. antarctica) is very much commoner in the yellow snow than the other, 
of which, indeed, only very few individuals were seen. Specimens of 
беоне Йа antarctica were always to be found to the number of several in 
every sample of yellow snow examined (ef. Pl. 11. photographs 1 & 6). 
The most prominent feature of this organism lies in the possession of six 
longitudinal wing-like extensions (briefly referred to as the wings in the 
subsequent description) of the wall, which run in a perfectly straight manner 
from one end of the cell to the other (Pl. 10. figs. 7-11). The six wings 
are placed at equal intervals round the circumference of the cell, so that they 
form angles of 60° with one another ; this is very well seen in individuals 
viewed from the end (i.e. in optical section, fig. 11), which have a very 
characteristic stellate appearance. Ordinarily, however, the cells are seen 
from the side, their general shape being oval, while the wings appear as 
follows (figs. 7, 10, 12): two of them lie flat with reference to the sub- 
stratum and present themselves as lateral extensions (fig. 7, 7 & 2) of the 
body of the cell, each of them about one-half the width of the latter ; two 
further wings (7. e. those projecting towards the observer, fig. 7, 3 & 4) 
appear as arched lines running over the surface of the cell from one end to 
the other and most obvious at a high focus, whilst at a lower focus two other 
longitudinal, arched lines (representing the pair of wings running on the 
under side of the cell) are visible £. In no case have I observed more or less 
than six wings. The actual behaviour of the wings at the two ends of the 
individual proved rather difficult to determine, but I think there can be 
по doubt that they run as follows :—It appears that one pair of opposite 
wings (which may be termed the principal wings) runs equatorially: round 
* Storage of fat is also found in Pleurococcus rufescens, which appears to be a species of 
Chlorosphera, А full diagnosis of Chlorosphera antarctica is given on p. 324-5. 
T Named after the ‘Scotia,’ the vessel which conveyed the members of the Scottish 
National Antarctic Expedition. 
| These wings are not shown in any of the figures representing side-views of the 
organism. 
