178 МВ. С. $. WEST ON THE FRESHWATER ALGÆ 
a species which occurs on maritime rocks about the tide-limits. It is, how- 
ever, distinguished by its thicker and much straighter trichomes, by the 
conspicuous constrictions between the cells, and by its free-floating habit. 
О. Tanganyike is a remarkable species and has undoubtedly a closer affinity 
with O. subuliformis than with any other known species of the genus. So 
striking is this resemblance, and so different is О, Tanganyike from other 
species of the genus, that one feels justified in suggesting that these two species 
have had a common origin, О. Tanganyike having acquired certain distinctive 
characters as a result of its adaptation to a pelagic existence. 
328. OSCILLATORIA SUBBREVIS, Schmidle, т Engl. Bot. Jahrb. xxx. (1902) 
р. 243, t. 4. fig. 7. 
Forma major ; crass. trich. 10-10°5 p. 
Tanganyika.— [|n swamp, Mbete (28 Sept. 1904 ; no. 108). 
The specimens from Tanganyika are in perfect agreement with Schmidle's 
species except for the thickness. The trichomes are straight, with un- 
attenuated and bluntly rounded extremities, and the cells are exceedingly 
short. The transverse cell-walls are bent as in specimens of O. subbrevis 
which I have recorded from Barbados in the West Indies (vide Journ. Bot. 
xlii. (1904) p. 292), some of them being concave and some convex to the apex 
of the trichome. The dark disc-shaped masses of intercellular (?) substance 
occur at irregular intervals along the length of the trichome. 
329. OSCILLATORIA FORMOSA, Bory, Dict. Cl. Hist. Nat. xii. (1827) p. 474; 
Gomont, in Ann. Sci. Nat. 7° sér., Bot. ху. (1892) p. 230, t. 7. fig. 16. 
Crass. trich. 4—4:2 д. 
Tanganyika.— Dredged from a few fathoms, near Kala (19 Nov. 1904 ; 
no. 171). 
330. OSCILLATORIA CORTIANA, Meneghini, 1. с. p. 8 ; Gomont, 1. е. p. 231, 
t. 7. fig. 17. 
Crass. trich. 7-1:5 д. 
Tanganyika.—In plankton, near Maswa (14 Jan. 1905; по. 11). 
Previously recorded only from thermal waters in Italy and Hungary. 
Genus SPIRULINA, Turp. 
331. SPIRULINA TENUISSIMA, Witz. Alg. Decad. xiv. (1836) no. 131 ; Tab. 
Phyc.i. р. 26, t. 37. fig. 4.—8. subsalsa, Ersted (1842); Gomont, 1. с. p. 253, 
t. 7. fig. 32. 
Nyasa.—On stones on shore, Domira Bay (19 June, 1904 ; no. 17). 
332. SPIRULINA LAXISSIMA, sp. п. (Pl. 9. fig. 6.) 
Trichomata angustissima, solitaria, inter algas pelagias sparsas, in spiram 
laxissimam regularem diametro 4°5-5°3 ш equaliter contorta, anfractibus 
17-22 р inter se distantibus; apicibus trichomatis rotundo-obtusis ; cyto- 
plasmate pallide #rnginoso et homogeneo, sine granulis. 
