FRESHWATER ALG^E OF THE SOUTH ORKNEYS. 131 



OSC1LLA TORI A CE^E. 



46. OSCILLATORIA BREVis, Kiitz. ; Gomont, Oscillariees, Ann. Sci. Nat., Sot., xvi., 

 p. 249, pi. vii.,figs. 14-15. 



Sample 10, rather rare. 



47. OSCILLATORIA SPLENDIDA, Grev. ; Gomont, Oscillariees, Ann. Sci. Nat., Bot., xvi., 

 p. '244, pi. vii., figs. 7-8. 



Sample 10, rather rare. 



48. OSCILLATORIA SUBTILISSIMA, Kiitz., Tab. Phyc., i., 1845-49, p. 27, tab. xxxviii., 

 fig. 7. 



Sample 10, rather rare. 



49. OSCILLATORIA TENUIS, Ag. ; Gomont, Oscillariees, Ann. Sci. Nat., Bot., xvi., 

 p. 240, pi. vii., figs. 2, 3. 



Samples 10. 11, and 15, rather rare. 

 Forma sordida, Kiitz., was also present. 



50. SPIRULINA SUBTILISSIMA, Kiitz., Phyc. gen., 1843, p. 183 ; Rabenh., Fl. Europ. 

 Alg., ii., 1865, p. 93; Gomont, Oscillariees, p. 272, pi. vii., fig. 30. 



Sample 10, rather common. 



NOSTOOAOE2E. 



51. ISOCYSTIS INFUSIONUM (Kiitz.), Borzi, Nuov. giorn. hot. ital., x., 1878, p. 468. 

 Samples 8, 11, 13, 15, and 17, rather common. 



52. NOSTOC MINUTISSIMUM, Kiitz., Phyc. gen., p. 204 ; Rabenh., FL Europ. Alg., 

 ii., 1865, p. 162. 



Samples 10 and 11, rather common ; 1 and 3 (yellow snow !), rare. 



RIVULARIACE^E. 



53. CALOTHRIX ^RUGINEA, Thuret ; Bornet et Flahault, Nostocacees heterocystees, 

 1886-88, p. 358. 



Sample 1 4, isolated. 



Diam. cell =9-11 M. Only one group of filaments was seen, and the determination 

 is therefore somewhat doubtful. C. seruginea is a marine form, but the habitat from 

 which sample 14 came would be likely to harbour marine forms. 



E. DIATOMACE^E (Bacillarieje). 



54. MELOSIRA VARIANS, Ag., Consp., 1830, p. 64; Rabenh., Fl. Europ. Alg., i. 

 1864, p. 40. 



Sample 9, rather rare. 



