OF THE THIRD TANGANYIKA EXPEDITION. 193 
Figs. 20. Staurastrum limneticum ; 21. S. tohopekaligense; 22 & 23. Surirella Malombe ; 
24 & 25. Surirella Füllebornii, var. ; 20. Melosira nyassensis; 27. Mass of decom- 
posing organic matter, probably excreta; 28. Mass of decaying organic matter, 
largely derived from Blue-green Alge. 
Note.—The quantity of decaying organic matter in the plankton of Victoria Nyanza is 
rendered very obvious by the numerous dark, ill-defined patches in the photographs. 
PLATE 4. 
Photomicrographs of plankton from Tanganyika. 
Figs. 1-13 x 100; figs. 14-17 x 200. 
Figs. 1-3. Spherocystis Schroeter’; 4 & 5. Hyalotheca mucosa. Figs. 1-5 represent plankton 
from the River Lofu near its entrance to Tanganyika. 
6. Oocystis lacustris; 7 & 8, Nitzschia nyassensis. (This Diatom occurred in countless 
myriads in plankton collections from certain parts of Tanganyika. It is of great 
length and very slender, much resembling the elongated varieties of Synedra Acus, 
to which plant it should possibly be referred.) 
The delicate curved lines in the photograph represent one of the minute plankton- 
species of the genus Lyngbya. 
9. Nitzschia nyassensis; 10 & ll. Anabena Flos-aque, var. circularis; 19 & 13. 
Glenodinium Pulvisculus. 
The dominating feature of this plankton is the short and much coiled variety of 
Anabena Flos-aque. In this respect the plankton is remarkably similar to certain 
collections from Nyasa (vide Pl. 2. figs. 15 & 16). 
14 & 15. Anabena Flos-aque, var. circularis; 15 shows very clearly the terminal 
heterocysts. 16 & l7. Glenodiniumn Pulvisculus. 
PLATE 5. 
Figs. 1-2. Spirogyra equinoctialis, sp. п. x 500. 1, single vegetative cell showing chloro- 
plasts; 2, male and female gametangia, with zygospore in greatly swollen female 
gametangium. 
3-4. Debarya africana, sp. п. X 500. 3, zygospore enclosed within the gametangia 
and conjugating-tube; 4, junction of vegetative cell (¢.v.) and gametangium (y.), 
showing thickened walls of latter with curious pit-like structure in the end- wall, 
. Pediastrum Tetras, (Ehrenb.) Ralfs, var. longicorne, Racib. x 520. 
. P. Tetras, (Ehrenb.) Ralfs. x 520. Curious coenobium of three cells. 
. Crucigenia tetracantha, sp. п. х 500. 
Figs. 8-9. Celastrum compositum, sp. n. X 520. 8, small coenobium of eight groups of 
three cells each ; 9, much larger ccenobium. 
Fig. 10. Palmophyllum foliaceum, sp. п. th., thallus, x 100; c., а few of the minute green 
cells, x 500. 
Figs. 11-18. Sphinctosiphon polymorphus, gen. et sp. п. 11, young colonies, x 100; 19, older 
and more elongated colony showing a few slight constrictions, x 100; 13, small 
portion of colony, x 520. 11 & 12 are only drawn in outline to show the hollow 
thallus. 
14-17. Chodatella subsalsa, Lemm. X 500. 15, cell containing two daughter-cells ; 
16 with four, and 17 with eight undeveloped gonidia (autospores). 
Fig. 18, Ankistrodesmus nitaschiotdes, sp. n. х 500. 
19. Pediastrum simplex, Meyen. х 500. Small 4-celled cenobium in which one cell 
has been aborted. 
LINN. JOURN,—BOTANY, VOL, XXXVIII. О 
Fig. 
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