OF THE THIRD TANGANYIKA EXPEDITION. 91 
Stephanodiscus, and Surirella were conspicuous. А few species of Navicula 
were not uncommon and Nitzschia nyassensis was frequent. Surirella Nyasse 
and S. bifrons were very characteristic, the former being a large and hand- 
some species which is apparently peculiar to this lake. 
Some of the collections, more especially nos. 15 and 16, were remarkable 
for the prodigious abundance of a form of Anabaena Flos-aque. The other 
Myxophycem of importance were Lyngbya bipunctata and Glootrichia. longi- 
articulata, sp. n. 
А species of Peridinium, which Lemmermann has described as P. africanum, 
occurred abundantly in some/ sf the material. 
Phytoplankton of Victoria Nyanza.—This large sheet of water extends from 
0° 95! N. to 39 S. and from 31° 45! to 34° 45 E., occupying an area of 
32,167 square miles. Its greatest length is 180 miles and its greatest width 
208 miles, its height above the sea being about 3800 ft. The depth is very 
variable, from about 6 ft. (at 2 miles from the shore) in Speke Gulf in the 
south to 300 ft. towards the middle, and 620 ft. near the eastern shore. 
The material was colleeted in April 1905, and was decidedly rich in 
Chlorophycez, especially Protococcoidew and Desmidiaces. ОЁ the latter, 
Staurastrum limneticum and S. tohopekaligense occurred in great abundance, 
and S. leptocladum forma africanum, S. brevispinum var. inerme, forms of 
S. gracile, and Cosmarium moniliforme were fairly common. The Proto- 
coccoidess were both abundant and of diverse character. Conspicuous were 
numerous forms of Pediastrum simplex and large cœnobia of Colastrum 
reticulatum and С. cambricum var. nasutum. Calastrum compositum 15 a 
previously undescribed species in which the grouping of the cells is very 
peculiar. Fine colonies of Dimorphococcus lunatus were not uncommon, and 
the colonies of Selenastrum gracile were the largest and best-developed I have 
ever seen. Closteriopsis longissima, which was present in the material from 
Lake Nyasa, and which is known from the plankton of several parts of 
Europe, was frequent, and Sphinctosiphon polymorphus is a new genus of the 
Ра|теПасе in which the mature colonies assume a vermiform character. 
The Diatoms were relatively few in number, but included a few fine species 
of Surirella, such as S. Füllebornii and S. Маот и», a large new species of 
Cymatopleura (C. Nyanse, sp. n.), and several species of Cyclotella and 
Melosira. 
The Myxophyceæ were poorly represented except for a few of the 
Chroococcaceæ. Two species I have considered to be new, Lyngbya circum- 
creta and Dactylococcopsis africana. Only a few fragments of a species of 
Anabæna were observed, but this may be due to the season of the year, as this 
genus was abundant in Tanganyika and Lake Nyasa later in the year. 
Of the Peridinieæ, a curious reduced form of Ceratium Hirundinella was 
