FRESHWATER ALG^E OF THE SOUTH ORKNEYS. 113 



same general shape and the cell-contents are often quite identical, there being two 

 terminal globules of fat with intermediate granular protoplasm (fig. 27) ; a pyrenoid 

 could not be made out. These cells, however, differ from those of C. brevispina in 

 three prominent respects: they are always of smaller dimensions (length, 13-15 /x), 

 they have a perfectly smooth, rather thin membrane devoid of spines, and the ends are 

 commonly more or less pointed (fig. 27) and never rounded off to such a marked extent 

 as is the case in C. brevispina (cf. even fig. 28 with figs. 25, 26). Were it not for the 

 difference of shape and the absence of all intermediate stages, these cells might be 

 regarded as young individuals of the latter ; but as it is, this view is scarcely permissible. 

 Similar though somewhat larger cells appear to have been observed by Lagerheim l in 

 red snow from Mount Pichincha in Ecuador ; he suggests that they may belong to some 

 member of the Volvocinese. It seems much more likely, however, that they represent 

 a species of Oocystis. In one or two cases a considerable number (about sixteen) of 

 these cells was observed lying within a common mucilaginous investment, which would 

 point to some species like Oocystis lacustris, Chocl., or 0. glceocystiformis, Borge. 

 There are further resemblances to 0. lacustris in the pointed shape of the cell, in the 

 (probably ?) single chloroplast, and in the occurrence of oil-drops in the latter species ; 2 

 also in the very feeble thickening of the ends of the cells in O. lacustris? a feature 

 which is much more pronounced in other species of the genus. For these reasons I am 

 inclined to regard the cells shown in figs. 27 and 28 as merely a form (f. nivalis) of 

 O. lacustris, Chod., characterised by the prominent storage of fat; 4 the cells, which 

 Lagerheim observed, may possibly belong to the same species. 



(h) SPH^ROCYSTIS SCHROETEEI, Chod., f. nivalis, n. f. (PI. II., phot. 2, S). 



In sample No. 3 of the yellow snow an organism (text fig. 1, F and G, p. 122) was 

 very abundant, which seems to be referable to the genus Sphivrocystis of Chodat. 5 This 

 form consists of larger or smaller groups of round or oval cells (text fig. 1, F). green 

 in colour and with granular contents, embedded in very soft mucilage, the outline of 

 which is often irregular, but sometimes roughly circular (particularly in the case of the 

 smaller colonies). The cells are separated by considerable intervals from one another, 

 and mostly show a very uniform distribution (text fig. 1, F) ; the intervening mucilage 

 is quite structureless and invisible. Each cell has a delicate bounding membrane of its 



1 Lagerheim, "Schneeflora ties Pichincha," Ber. Deutsch. Hot. Ges., x., 1892, p. 525, footnote 2 : "Zahlreiche ovale 

 Zellen, 6-10 n dick und 10-20 ^ lang, welche grunen Inhalt und an den Enden je einen zuweilen rothlichen (Eltropfen 

 fiihrten. Sie lagen immer isoliert und konnten nicht zur Entwickelung gebracht werden." 



2 Cf. Chodat, "Etudes de Biologie lacustre," Bull. Herbier Boissier, v., 1897, p. 296 ; also Algues vertes de la Suisse, 

 Berne, 1902, p. 190, fig. 105. 



3 Chodat's figures in most cases give very little indication of this thickening, which was not to be found iu the 

 Antarctic specimens. The latter may possibly have been relatively young individuals, a view which is supported by 

 the thinness of the walls. 4 See also p. 124. 



5 Chodat, " Etudes de Biologie lacustre," Bull. Herbier Boissier, v., 1897, pp. 292-295, pi. ix. ; also Algues vertes de la 

 Suisse, Berne, 1902, pp. 114, 115, fig. 53. According to G. S. West (Journ. Linn. Soc., Bot., xxxix., 1909, pp. 75, 76) 

 Sphserocystis schroeteri, Chod., and Tetraspora lacustris, Lemm., are synonymous (cf. also Chodat, Alg. vertes, p. 115). 

 VOL. III. 15 



