THE YAN YEAN RESERVOIR, VICTORIA, 85 
its Desmid-flora it compares very well with the lakes of the western British 
lake-areas. The Yan Yean Reservoir furnishes another instance of a rich 
Desmid-plankton occurring in a lake situated on the Older Paleozoic formations 
and receiving the drainage from extensive outcrops of these old rocks, A portion 
of the drainage, as is so often the case in mountainous, Older Paleozoic areas, 
is also derived from outcrops of igneous material. 
In the complete absence of Fragilaria and Asterionella, and of the star- 
dispositions of the frustules of Tabellaria, the phytoplankton differs con- 
spieuouxly from the European plankton, but agrees with the known plankton 
of the great African lakes. 
Iu the plankton of the Yan Yean Reservoir there are three distinct 
phases :— 
I. ,Vov.-Jan. (beginning of warm period ).— Melosira granulata and 
Dinobryon are the chief constituents, together with a few of 
the Protococcoideæ (such as Pediastrum duplew var. clathratum 
and Æudorina elegans). 
II. Feb.—May (warm period or summer phase).—Desmids dominant, 
with a little Melosira granulata. 
IIT. Sune—Oct. (cold period). — Crustacea dominant; phytoplankton 
almost absent. 
The summer phase of the plankton (from Feb. to May), which in most 
European and North American lakes is dominated by Blue-green Algæ, ix 
here dominated by Desmids (as in many lakes of the British area) and by 
Melosira granulata. The latter is an exception to most of the freshwater 
Bacillarieæ in having its maximum in the warmest period of the year. 
Out of 104 species and 16 varieties observed in the phytoplankton, 
23 species and 5 varieties were exclusively confined to it, not having been 
seen from any other part of the entire drainage area. 
2. The MICROPHYTIC BENTHOS or littoral Alga-flora of the Yan Yean 
Reservoir was richer in species than the phytoplankton and contained many 
interesting types. Many species common to the plankton and the benthos attain 
first а marimum in the plankton and subsequently а maximum in the benthos, 
the time which elapses between these two maxima varying from three to 
eight weeks. 
There are three phases in the benthos during the year, but. these are not so 
marked as the phases of the phytoplankton. They may be stated аз 
follows :— 
I. Nov.—J«n. (vernal rise of temperature).— Dominance of Oedo- 
goniaceæ and Zygnemaceæ (mostly in the fruiting condition). 
Many Desmids present, and some species abundant. — Peridinium 
and Dinobryon frequent. 
