THE YAN YEAN RESERVOIR, VICTORIA. 65 
(very common in Apr. 1905 and Feb. 1906) ; also rare at the weedy margins 
(Apr. and May, 1905). 
Cosmarium Hardyi is a very characteristic species. The form of its semi- 
cells, with their granulate lower margins, and the numerous central scrobicula- 
tions easily distinguish it from any others with which it might be confused. 
Its great thickness is also a distinctive feature. 
39. CosMARIUM AMPLUM, .Vordst. in Dot. Notis. (1887) p. 163 ; Le, (1888) 
р. 03, t. 6. fig. 20. 
Long. 130-135 p ; lat. 92-97 u; lat. isthm. 28-29 д. 
flab. Pool in the Yan Yean Catchment area, common (Sept. 1907). 
Genus XANTHIDIUM, Ehrenb. 
56. XANTHIDIUM HASTIFERUM, W. D. Turn, in Journ. Roy. Міст. Soe. 
ser. 2, v. (1885) p. 938, t. 15. fig. 20.—X. Antilopæum var. angulatum, 
Josh. (1886). 
Forma cellulis latioribus, apicibus paullo elevatis; spinis apicalibus 
reductis, singulis vel binis, nonnunquam papillatis vel rarissime nullis. 
Long. s. spin. 45-46 ш: lat. s. spin. 48-50 р, с. spin. 85-98 ш; lat. 
isthm. 10-11 y. 
Нар. Yan Yean Reservoir, in the plankton (Mar. and April, 1905) and at 
the weedy margins (Маг., May, and June, 1905). 
This form is of interest as it connects the typical plant with the New 
Zealand var. inevolutum, Nordst. (К. Sv. Vet.-Akad. Handl. xxii. по. 8 (1880), 
р. 43, t. 4. Во. 24). It is quite possible that the semicell upon which Nordstedt 
founded his New Zealand variety belongs to the same form as the Victorian 
specimens, as semicells of the latter were occasionally destitute of the shorter 
apical spines. 
Genus ARTH RODESMUS, Ehrenb. 
37. ARTHRODESMUS Ixcvs, (Bréb.) Hass. Brit. Freshw. Alg. (1845) p. 357; 
Ralfs, Brit. Desin. (1848) р. 118, t. 20. figs. 4 a-d. 
Two forms were noticed in moderate abundance. 
Forma а, Large form of fairly typical shape, with strong divergent spines. 
Long. s. spin. 25 д; lat. s. spin. 26-28 р, c. spin. 53-56 ш; lat. isthm. 6 р. 
Forma b. Small form somewhat resembling A. phimus, W. В. Turn., var. 
occidentalis, W. & G.S. West (in Trans. Roy. Irish Acad. xxxii. (1902) p. 58, 
t. 2. fig. 17), but with a straight apex. 
Long. 16 p; lat. $. spin. 17-18 р, c. spin. 22-23 ш; lat. isthm. 4:5-5 д. 
Па. Yan Yean Reservoir. Both forms occurred in the plankton and at 
the weedy margin of the lake; forma « was much more frequently met with 
than forma ^. 
LINN. JOURN.— BOTANY, VOL. XXXIX. F 
