THE YAN YEAN RESERVOIR, VICTORIA. 7 
Class BACILLARIEZE. 
Order CENTRIC. 
Family RHIZOSOLENIACEZE. 
Genus RHIZOSOLENIA, Ehrenb. 
61. RuizosoLENIA MORSA, И”. у G. S. West, in Trans, Roy. Irish. Acad. 
xxxiii. sect, В (1906), p. 109, t. 11. figs. 5-7.—R. eriensis, M. L. Smith, 
var. morsa, W. y G. S. West, in Trans. Roy. бое. Edin. xli. part iii. (1905): 
р. 509, t. 6. fig. 23. 
Lat. valv. 5-9 ш; long. set. 18-22 ш. (Pl. 8. figs. 15-16.) 
Hab. Yan Yean Reservoir, in the plankton (Jan. 1906). 
This Diatom was not uncommon in the January plankton, but no trace of 
it was observed in any of the other collections. It thus appears in the 
plankton only when the temperature of the surface water is at its highest 
(74° F. 22:03? C.) In the possession of the peculiar excavated extremities. 
the specimens exactly agreed with those which occur in the summer plankton 
of the lakes of the western British area, but they were all proportionately 
smaller with shorter bristles. 
It is probable that the vegetative period of R. morsa lasts only for about 
five or six weeks in the warmest part of the year, and as I have never yet seen 
a single individual except from a purely limnetic habitat, the vegetative 
phase appears to be confined to the plankton. At its conclusion, resting- 
spores are formed, which presumably remain dormant for an extended period 
until the requisite conditions for germination again supervene, but practically 
nothing is known concerning the resting-spores during the lengthy period 
they appear to be quiescent. 
Order PENNATÆ. 
Family EUNOTIACEZ. 
Genus EUNOTIA, Ehrenb. 
62. EUNOTIA MAJOR, ( W. Sm.) Rabenh., var. BIDENS, (Greg.); Van Heurck, 
Synops. Diat. Belg. t. ЗА. fig. 15.—Himantidium bicens, Greg. 
This Diatom was very common among the Yan Yean weeds, and the valves 
exhibited a great variability of size. Some of the tiny specimens were only 
36 ш in length, whereas the largest reached a length of 158 р, a much more 
normal size for forms of Lunotia major. 
