OF THE THIRD TANGANYIKA EXPEDITION. 157 
Large forms : long. 42-05 ш: lat. 9°5-15°5 ш; lat. ар. 372-58 p. Valves 
oblong or oblong-lanceolate, with rostrate apices. (РІ. 8. fig. 12.) 
Tanganyika.— Plankton, Kituta Bay (26 Aug. 1904 ; no. 81), Komba Вау 
(11 Oct. 1904 ; no. 135), and near Kirando (1 Dec. 1904 ; no. 175). 
The bifid stauros and the longitudinal septa (or diaphragms) in the apical 
parts of the valves are the distinguishing features between this genus and 
Stauroneis. The specimens observed were all obtained from the fine surface 
plankton, and they reached almost twice the size of any previously recorded 
examples. The strive were very fine, about 23 or 25 in 10 p. 
Genus VANHEURCKIA, Zréb. 
935. VANHEURCKIA RHOMBOIDES, ( Ehrenb.) Bréb. Monogr. p. 4 (1869); 
Van Heurck, Synops. Diat. Belg. p. 112, t. 17. figs. 1, 2.—Navicula rhomboides, 
Ehrenb. ; W. Sm. Brit. Diat. i. p. 46, t. 16. fig. 129. — Frustulia rhomboides, 
De Тот. 
Victoria Nyanza.—In swampy pools, near Bukoba (20 Apr. 1905 : no. 251). 
Var. sAXONICA, (Rabenh.) G. 5. West.—Frustulia saxonica, Rabenh. Navi- 
cula crassinervia, Bréb. in W. Sm. Brit. Diat. i. p. 47, t. 31. fig. 271. 
Tanganyika.—In swamp, Mbete (28 Sept. 1904 ; no. 108). 
Victoria Nyanza.—In swampy pool, near Bukoba (20 Apr. 1905 ; no. 618). 
936. VANHEURCKIA VULGARIS, (Thw.) Van Heurck, Synops. Diat. Belg. 
p. 112, t. 17. Но. 6.— Colletonema vulgaris, Thw. 
Tanganyika.—ln plankton, Lofu River (5 Oct. 1904 ; no. 123). 
Genus GYROSIGMA, Hass. 
237. GYROSIGMA ATTENUATUM, (Kütz.) Cleve, Synops. Navic. Diat. 1. (1894) 
p. 114.—Pleurosigma attenuatum, W. Sm. Brit. Diat. i. p. 68, t. 22. fig. 216. 
Tanganyika.—In plankton, near Kassanga (14 Nov. 1904 ; по. 159), near 
Kala (19 Nov. 1904 ; no. 170), near Maswa (14 Jan. 1905; no. 211), and 
near Baraka (24 Feb. 1905 ; по. 240). 
The specimens observed were all considerably shorter than is usual 
in this species. The apices of the valves were not quite so attenuated as in 
European examples. 
238. GYROSIGMA NODIFERUM, (Grun.).—Pleurosigma nodiferum, Grun. 
Arct. Diat. p. 59. P. Spenceri, W. Sm., var. nodifera, Van Heurck, Synops. 
Diat. Belg. (1885) p. 118, t. 21. fig. 13; Cleve, Synops. Хате. Diat. 1. (1894) 
p. 117. 
Long. 152 ш; lat. 17 p. 
Tanganyika.—In plankton, near Kala (19 Nov. 1904 ; no. 170). 
The general form of this species and the curious elongated, oblique central 
nodule appear to me to be quite distinctive. 
