FRESHWATER ALG^E OF THE SOUTH ORKNKYS. 103 



descriptions, 1 by the thallus consisting of a central group of irregularly arranged cells 

 from which short filaments radiate out at the periphery. Of this feature Protoderma 

 In-oiriiii shows nothing, the edge of the thallus in all cases presenting just as irregular 

 an arrangement of the cells as obtains in the middle. P. broivnii also differs from the 

 other species of the genns in not being an epiphyte (cf. however p. 127). Rabenhorst's 2 

 figure and description of P. ririJe, Kiitz., however, give no indication of any regular 

 arrangement of the cells, and the same is true of Migula's recent description, which 

 even refers to the cells as being " orduungslos " and " nicht in Reihen." : The latter's 

 description of Protoderma also recalls the Antarctic form, in that he speaks of the thallus 

 as "schleimig." This character is also referred to in Hansgirg's description, 4 which 

 further contains a statement (on p. 225) as to the occurrence of oil drops in the cells. 

 It will therefore be evident that all the characteristic features of P. broimii have already 

 been referred to in the descriptions of P. viride, and it may ultimately prove to be but 

 a form of the latter. For the present, however, it seems best to keep it as a distinct 

 species, characterised by the irregular arrangement of the cells, the mucilaginous and 

 granular character of the walls, and the frequent presence of fat in the cell-contents. 5 



(b) CHLOROSPH.^RA ANTARCTICA, n. sp. (PI. I., figs. 2-6; PI. II., phots. 1, 3, 5, 6, C). 



The next most abundant form is a new species of Chlorosph&ra, which may be 

 called C. antarctica, n. sp. (PI. I., figs. 2-6). This is found either in the form of large 

 isolated cell (figs. 2, 6) or as groups of smaller cells, commonly in fours or sometimes 

 larger numbers (PI. I., fig. 3) ; the average diameter of the cells varies between 11 and 

 26 M, although smaller and much larger cells were also observed. The cells are provided 

 with a well-defined rather thick membrane, which, especially in the case of the isolated 

 cells, is often surrounded by a wide spherical sheath of transparent mucilage (PI. II., 

 pilots. 1, 3), to the outer edge of which numerous small foreign particles were generally 

 adhering (PI. I., fig. 2). The isolated cells were mostly more or less spherical in shape, 

 while those forming groups were somewhat angular, probably as a result of mutual 

 pressure. In many cases an almost spherical chloroplast could be made out in the cells 

 without much difficulty ; this chloroplast is only interrupted on one side of the cell by a 

 small circular aperture, through which a small round body (in all probability the pyrenoid) 

 can be seen (PI. I., fig. 2). Starch is mostly present in small quantities in the smaller cells, 

 but is often scarcely to be found in the larger ones. On the other hand, large masses 



1 G. S. West, The British Freshwater Algse, Cambridge, 1904, p. 204, and fig. 83 A-c ; N. Wille, "Conjugate and 

 Chlorophycec-r," in Engler and Prantl, Die natiirl. Pflanzenfamilien, Nachtr. z. 1 Teil, 2 Abteil. (Leipzig, 1909), p. 89 ; 

 cf. also Hansgirg, Prodrtmms il. Algenjlora v, Bohmen, i. (Prague, 1886), p. 22. 



'- L. Rabenliorst, Flui-'i europa n ulijuritin cnyM.r diilfis et submari/ur, iii., Lipsia^, 1868, pp. 288 and 307. 



3 W. Migula, Kryptogamenflora von D<mls<-hl<ntil, Deittsch-Osterreieh uitd der Si-hiiviz, n., 1 Teil, Gera, 1907, p. 747 ; 

 -/. .-ilso Wille, loc. cit, 1 Teil, 2 Abteil., 1*1)7, p. 78. 



4 " Meist schliipferig," according to Hansgirg, loc. cit., p. 224. 



5 A full diagnosis of Protn.l. rum lirmi-nii will lie found on p. 126. It seems very probable that the form shown by 

 Wittrock (" Om snons och isens Flora," Inc. cit.) in his fig. 17 (pi. iii.) belongs to this species, although the cells are more 

 regularly arranged than in my form. 



