THE YAN YEAN RESERVOIR, VICTORIA. 19 
and Wesenberg-Lund * state that Dinobryon is a prominent feature of lakes 
of higher altitudes in which the temperature of the water is never very high. 
In the Danish lakes, Wesenberg-Lund + also finds the maximum to oceur in 
May. In the ©“ Altwüsser? of the Danube, Drunnthaler t records the 
maximum of D. Sertularia var. thrysoideum as occurring in January, that of 
D. cylindricum var. divergens in May, and that of D. sociale in June. In the 
Yan Yean plankton the maximum of D. cylindricum (and also its var. 
divergens) occurs from 18—20? C., whereas in the European plankton the 
maximum is attained at а temperature below 15° С. In the lakes of tropical 
Africa, with a mean surface temperature of over 20° C., Dinobryon is entirely 
absent $. 
Peridiniez.— Only one species of this group occurred in the plankton. 
This form, Peridinium Volzii var. australe, which is of great interest from a 
classificatory point of view, had two maxima, the first in November, with a 
temperature of 15? C., and the second in February, with a temperature of 
24-4? C. 
Chlorophycez.— Fragments of Mougeotia were not uncommon, but no coiled 
filaments were observed such as occur in the British freshwater plankton, 
The dominant Chlorophycee are Desmids. From February to May the 
plankton has all the characters of a Desmid-plankton. They attain their 
maximum from February to April, at а time when the temperature of the 
water is at its highest and when the Crustacea are least in evidence. The 
most conspicuous of these Desmids is Mierasterias flardyi, а handsome 
species which up to the present is only known to occur in this one lake |. 
It is never absent from the plankton, and appears to have two maxima : the 
first т April (temp. 17-8? C.), and the second in December (temp. 20° (1. 
Cosmarium Hardyi, with its maximum in April, and. C. contractum are both 
conspicuous constituents of the plankton, especially the former. Staurastrum 
leptacanthum is common from February to April, and the extraordinary 
S. victoriense, although always a scarce constituent, was only absent from 
the plankton in September. In all, 58 species of Desmids occurred in the 
plankton, many of them abundantly. Volvox aureus and Eudorina elegans 
* C. H. Ostenfeld & C. Wesenberg-Lund, in Proc. Roy. Soc. Edin. xxv. part xii. (1906) 
p. 1098. 
T C. Wesenberg-Lund, * Studier over de Danske Süers Plankton," Dansk. Ferskv.-Biol. 
ор. 5, Kjóbenhavn, 1904, p. 115 ( Summary,” p. 26). 
і J. Brunnthaler, in Verh. der k.k.zool.-bot. Ges. Wien (1907), p. 185. 
$ G. S. West, in Journ. Linn. Soc., Bot. xxxviii. (1907) p. 84. 
| This species may occur in other parts of Victoria, or of Australasia, but Mr. Hard y's 
careful collections have failed to reveal its presence in any other part of the Yan Yean 
drainage area. Should Wicrasterias Hardyi be restricted to this one lake, it will afford a 
parallel to the occurrence of М. Murrayi, W. & G. S. W est, in the plankton of Loch Ruar, 
Sutherland. (Vide W. & G. S. West, in Journ. Linn. Soc., Bot. xxxv. (1903) p. 538.) 
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