164 MR. G. S. WEST ON THE FRESHWATER ALG.E 
species, which he described from the plankton of Nyasa and the pools in the 
vicinity of that lake, but I am not convinced of its correct inclusion in the 
genus Nitzschia. On first examining it I took it to be a form of Synedra 
Lemmermannii, W. & С. S. West (“ Plankton of Some Irish Lakes," Trans. 
Roy. Irish Acad. xxxiii. (1906) p. 109, t. 11. figs. 1, 2), but the frustules are 
rot so straight as in that species, the markings not so distinet, and the poles 
much less capitate. The African forms were commonly a little curved, which 
is not surprising in such a long narrow Diatom, and in some of the collections 
they were often curiously bent (especially in nos. 52 and 150). In this species, 
and very probably in several other shorter ones, the genera Nitzschia and 
Synedra merge into each other. 
Family SURIRELLACEZ. 
Genus SURIRELLA, Turp. 
269. SuRIRELLA ROBUSTA, Ehrenb. in Ber. Akad. Berl. (1840) p. 215.— 
. nobilis, W. Sm. Brit. Diat. i. p. 32, t. T. fig. 63. 
Var. SPLENDIDA, (Hhrenb.) Van Heurck, Synops. Diat. Belg. 1885, p. 187, 
t. 72. fig. 4.—8. splendida, Kütz. Baciil. (1844) p. 62, t. 7. fig. 9. 
Tanganyika.—In plankton, Lofu River (5 Oct. 1904 ; no. 124). 
on 
270. SURIRELLA Ёйш„квовхп, О. Müll. in Engl. Bot. Jahrb. xxxvi. (1905) 
p. 30, t. 1. fig. 11. 
Victoria Nyanza.—In plankton, near Bukoba (18 Apr. 1905 ; по. 249). 
Var. ELLIPTICA, О. Mill, 1. е. p. 31, t. 1. fig. 18. 
Long. 216-250 p ; lat. 80-97 u. (РІ. 3. figs. 3, 4.) 
Victoria Nyanza.— With the typical form, but much more abundant (nos. 249 
and 252). 
971. SURIRELLA BIFRONS, ( Ehrenb.) Kütz. Bacill. (1844) p. 61. 
Var. TUMIDA, О. Müll. 1. с. p. 27, t. 1. fig. 2. 
Long. 98-160 ш ; lat. 46-58 p. 
Nyasa.—In plankton, Anchorage Bay (June, 1904 ; nos. 9 and 10). 
Victoria Nyanza.—In plankton, Bukoba (18 Apr. 1905 ; no. 249). 
Var. INTERMEDIA, О. Müll. l с. р. 27, t. 1. fig. 1. 
Nyasa.—In plankton, Anchorage Bay (June, 1904 ; nos. 9 aud 10). 
972. SunrRELLA MaLowma, О. Müll. 1. c. р. 84, t. 2. fig. 5 [inelus. forma 
acuta, О. Müll. 1. c. t. 2. fig. 7]. 
Long. 125-161 p ; lat. 70-74 p. (РІ. 3. figs. 2, 13, 14, 22, 23.) 
Victoria Nyanza.— Very abundantin the plankton, near Bukoba (Apr. 1905; 
nos. 249 and. 252). 
