FRESHWATER ALO^B OF THE SOUTH OKKNEY8. 105 



i 



i SCOTIKLLA ANTARCTICA, D. gCD. et 8p. (PI. I., figs. 7-17 I 



PI. II., phot*. 1, 4, 6, Sc). 



The two species so far considered are by far the most abundant forms in the yellow 

 snow 6ora, and the remaining members, although many of them not uncommon, 

 are quite aul>si<liury to them. Among the latter is a very striking unicellular 

 organism, whirh I regard as the type of a new genus, Scotiella. 1 I have observed 

 two species of this genus, one of which (S. antarctica, n. sp.) is very much commoner 

 in the yellow snow than the other, of which indeed only very few individuals were 

 seen. Specimens of S. antarctica were always to be found to the number of several 

 in every sample of yellow snow examined (<;/" PI. II., phots. 1, G). 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 oval cell to the other (PL I., 

 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, PL I., fig. 1 1), 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 (PL I., figs. 7, 10, 12) : 

 two of them He flat with reference to the substratum, and present themselves as lateral 

 extensions (fig. 7, 1 and 2) of the body of the cell, each of them about one half the 

 width of the latter; two further wings, i.e. those projecting towards the observer (fig. 7, 

 3 and 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 no doubt that they run as follows : It appears that one pair of 

 opposite wings (which may be termed the principal wings) runs equatorially round the 

 oval cell as a uniform expansion of the body (1 and 2 in figs. 7, 8, 9, and 11, p.w. in 

 fig. 8), this expansion being rather wider at the sides than at the two ends of the cells. 

 In the other two pairs of wings (lateral wings), the wings of each pair form an angle 

 of 60* with one another and with the principal wings, these pairs being 3, 4, and 5, 6 

 in fig. 11.* At the two ends of the cell the wings of each lateral pair become very 

 slightly arched out, and then dip in suddenly and meet together, so that a kind of 

 apparent sinus is formed at the two ends on either side of the principal wings (cf. fig. 7, 

 and especially figs. 8 and 9, which are oblique end-views of S. antarctica, showing only 

 the course of the wings). The customary position of an individual of S. antarctica is 



1 Named after the Stotia, the veasel which conveyed the member* of the Scottish National Antarctic Expedition. 

 1 Them wings are not shown in any of the figures representing cide-riews of the organism. 

 1 In an optical section, inch as fig. 11, there is nothing to distinguish the different wings from one another, and 

 the numbering u purely arbitrary for the purposes of description. 



VOL. III. II 



