THE YAN YEAN RESERVOIR, VICTORIA. 21 
although Melosira granulata occurs abundantly and is never absent from the 
collections. It is most conspicuous from November to April, and reaches its 
maximum in February, when the temperature of the water averages 21? C. 
Auxospore-formation took place in January ; that is to say, at approximately 
the period of highest temperature *. Хо coiled filaments were observed such 
as occur in the plankton of certain European lakes. Ahizosolenia morsa 
occurred abundantly in January (temp. of water 23:3? C.), but was not 
observed in any other month. As in the British plankton f, this Diatom is 
apparently a summer (or warm-water) species with a very brief vegetative 
period. Of the Naviculaceæ, Navicula bicapitata was common in November, 
and Vanheurckia viridula was scarce from April to July. Both these species 
are shore forms and occurred abundantly in the benthos ; but it is worthy of 
note that the plankton-specimens of the latter species were of much greater 
size than those observed from any other situation. Species of Gyrosigma 
are not infrequently met with in the freshwater plankton, but the species 
which occurred in the November plankton of the Yan Yean is of more than 
ordinary interest. It occurred very sparingly, and it is much more nearly 
allied to certain of the marine species of the genus than to any of the known 
freshwater species. For the present I have regarded it as possibly a variety 
of Gyrosigma elongatum (consult p. 79). Tabellaria flocculosa, although 
never frequent, was present in all the collections except those made in 
August. 
Myxophycee.—The remarkable scarcity of Blue-green Algz has already 
been commented upon. Oscillatoria Agardhii was common in July, and 
Chroococcus limneticus var. subsalsus occurred abundantly in April. There 
is no phase of the plankton in which Blue-green Algæ dominate such as 
occurs in so many European 1 and №. American lakes $. 
* In the report upon the plankton of Thingvallavatn, Iceland, C. H. Ostenfeld & 
C. Wesenberg-Lund record the auxospore-formation of Melosira islandica as commencing 
rather suddenly between the middle of December and the middle of January (temp. 1°- 
2° C.); vide Proc. Roy. Soc, Edin. xxv. part xii. (1906) p. 1117. Thisis in striking contrast 
to the auxospore-formation of М. granulata in the Yan Yean at a temp. of 25:3? C. 
t W. West & G. S. West, in Traus. Roy. Soc. Edin. xli. part iii. (1905) p. 509; Trans. 
Roy. Irish Acad. xxxiii, sect. В, part и. (1906) p. 109. 
i Consult В. Schröder, “ Das Pflanzenplankton preussischer Seen," Westpreuss. Bot.-Zool. 
Verein, Danzig (1900), p. 73; E. Lemmermann, * Das Phytoplankton einiger Plóner Seen," 
Forschungsb. Biol. Stat. Plóu, x. (1903) p. 126 ; K. v. Keissler, in Oesterr. botan. Zeitschr. 
(1906) no. 5-6, p. 4; Н, Huitfeldt-Kaas, * Planktonundersogelser Norske Vande,’ Chris- 
tiania (1906), p. 152; and many others. 
$ C. Dwight Marsh, in Bull. Wisconsin Geol. and Nat. Hist. Survey, Sci. ser, 3, xii. p. 15; 
and others. 
