OF THE THIRD TANGANYIKA EXPEDITION. 165 
This species was in great abundance and every intermediate stage was 
noticed between it and S. bifrons var. tumida. Many of the forms of S. bifrons 
var. tumida from Lake Nyasa might have been equally well named 5, Malombe. 
Much variation was also shown in the apiculation of the extremities. 
273. SvmmELLA Nyassa, O. Müll. in Engl. Bot. Jahrb. xxxvi. (1905) 
р. 33, t. 2. fig. 3 [inclus. var. Sagitta, О. Май. 1. с. t. 2. fig. 4]. 
Long. 359-382 p ; lat. max. 69-75 ш ; lat. ad med. 54-57 р. 
Муаза.— п plankton, off Vahambwera Point (24 June, 1904; no. 24), 
Deep Bay (24 June, 1904 ; no. 25), and off Karonga (1 July, 1904 ; no. 30). 
‚ This handsome species was very abundant and many intermediate states 
oecurred between the typical form as described by Müller and his var. Sagitta. 
It is a large species, which, so far as present observations go, appears to be 
confined to the plankton of Lake Nyasa. | 
Many of the frustules were thickly coated with attached Vorticelle (vide 
PI. 2. figs. 11, 12). 
274. SuRIRELLA PLANA, sp. п. (Pl. 8. fig. 5.) 
S. subparva ; cellula ut in visa aspectu valvulari ovato-elliptica ; pseudo- 
rhaphide recta et distincta ; costis validis subconfertis, circiter 3 in 10 р 
(29-30 in margine laterali unoquoque), transversis sed polos versus leviter 
radiatis, pseudorhaphidem extensis ; alis curtis juxta margines laterales. 
Long. 103 р; lat. max. 89 р. 
Tanganyika.—In plankton, near Ndauvie (7 Feb. 1905 ; no. 227). 
This Diatom was only noticed from one of the plankton collections. It 
should be compared with S. diaphana, Bleisch, and S. tenera, Greg. 
215. SURIRELLA LINEARIS, W. бт. Brit. Diat. i. p. 31, fig. 58 a. 
Victoria Nyanza.—Among Utricularia, near Bukoba (20 Apr. 1905; 
no. 613). 
976. SURIRELLA CONSTRICTA, Ehrenb. Мих. t. 14. fig. 37 (1854).—Navi- 
cula ? constricta, Ehrenb. Infus. 1838, p. 188, t. 21. fig. 17. 
Var. AFRICANA, O. Müll. in Engl. Bot. Jahrb. xxxvi. (1905) р. 32, t. 2. fig. 1. 
Long. 250-295 ш; lat. max. 42-45 p ; lat. min. 33-34 р. 
Tanganyika.—In plankton, Niamkolo (7 Sept. 1904 ; no. 88), near Sumbu 
(13 Oct. 1904 ; по. 138), and near Kassanga (14 Nov. 1904 ; no. 159). 
277. SURIRELLA OBTUSIUSCULA, sp. п. (РІ. 8. fig. 7.) 
5. parva : cellula ut in visa aspectu valvulari oblongo-elliptica, marginibus 
lateralibus leviter concavis (cellula levissime et gradatim constricta), polis 
obtusis ; pseudorhaphide recta vix distincta ; costis brevibus, transversis sed 
polos versus radiatis, 4 т 10 p (20-21 in margine laterali unoquoque) ; 
alis ad margines laterales ; cellula ut in visa aspectu cingulato oblonga, 
marginibus lateralibus in medio retusis, polis truncatis sed angulis rotundatis. 
