FRESHWATER ALGJE OF THE SOUTH ORKNEYS. 109 



individuals so bad in most cases, that only a brief description can be given. The cells 

 are oval, and of considerably smaller dimensions than those of S. antarctica ; in place 

 of the six wings of the latter the cells are provided with numerous longitudinal wings, 

 which generally have a somewhat spiral trend (fig. 18, and especially figs. 19 and 21). 

 The wings do not stand off from the body of the cell nearly as prominently as in 

 S. <(it/i'rf/fca, (c/. especially fig. 20, which is an oblique end-view of the organism). 

 Each of the wings is undulated (fig. 18), and this fact, together with the large number 

 of the wings, makes the cells present a notched crenate outline from whatever point 

 they are viewed (cf. figs. '20, 21). At the two ends of the cells the wings bend inwards, 

 and terminate in a shallow sinus (fig. 20, also 21 and 18). The wings are solid, as 

 in the other species, and appear as flat crenations in optical section (fig. 20). As 

 regards the contents of the cells of S. polyptera, in the few cases in which they could 

 be made out at all there appeared to be a single chloroplast with a prominent pyrenoid 

 (fig. 21); fat was not observed in the cell-contents of this species. Only one case of 

 possible reproduction was found (fig. 19); a cell of S. polyptera, in which the outline 

 of the wings had become obscure (visible, however, as delicate spiral lines in the right- 

 hand portion of fig. 19), contained a number of elongated protoplasmic masses, in one 

 of which a pyrenoid was prominent. This stage is possibly to be interpreted as 

 division of the contents of the individual to form a number of daughter-individuals ; 

 if this is so, it of course constitutes a marked analogy to the probable stage of 

 S. antarctica shown in fig. 17. It may be added that the individuals of S. polyptera 

 were not uncommonly found in groups of four or five, which would quite accord with 

 their being formed by subdivision of a mother-individual. 



S. polyptera is obviously of a more dubious character than S. antarctica. While 

 some doubt may justly be felt as to its independence (for it might be the zygospore 

 of some form ? 1 ), it is impossible to feel quite certain of its close affinity to S. antarctica, 

 and further observations may warrant its removal from the genus Scotiella. In view 

 of the bad definition of the wings in all the cells observed, I am inclined to think 

 that no normal individuals of S. polyptera were present in my material, and that 

 all the forms observed were either preparing for division or passing over into some 

 resting-stage. 2 



(c) PTEROMONAS NIVALIS, Chod. (PI. I., figs. 22-24, 31). 



Another form, of which, however, only very occasional specimens were met with in 

 the yellow snow material, is represented in figs. 22-24 and 31 of PI. I. This is almost 



1 I have not, however, met with anything to countenance this view. Lagertieim (" Schneeflora des Pichincha," 

 Ber. Deutsch. Bot. Ges., x., 1892, p. 529 ; also "Schneeflora in Lulea Lappmark," Hot. Centralbl., xvi., No. 11, 1883) 

 refers to oval cells (15^ broad and 30 /i long) as occurring in red snow from Amsterdamo (Spitsbergen). These 

 cells are described as having longitudinal ridges, and may possibly represent the same form as S. polyptera, or a 

 closely allied one. Lagerheim, however, regards these cells as probably being zygospores of Clilamydomonas lateritia 

 (cf. p. Ill, footnote 1). 



2 A diagnosis of Scotiella polyptera is given on p. 125. 



