The Genus Microcystis in Ceylon 65 
of its clathrate colonies, may at times closely resemble M. ceruginosa 
and M. ochracea (Brand) De Toni, but in dealing with these forms it 
is necessary to take into account the general or normal type of the 
colony and certainly on this basis M. pseudofilamentosa must be 
regarded as quite distinct. This species and M. stagnalis are remark¬ 
able examples of homoplasy with the elongated Tetrasporaceae. 
Loc. Tank Nuwarawewa at Anuradhapoora, Oct. 2nd. 
MICROCYSTIS MARGINATA (Menegh.) Kuetz.(4) 
Figs, g and h 
Colonies rounded or irregular, generally flattened and of more or 
less lenticular form, simple or in clusters not surrounded by a common 
colonial sheath. Margin of colonial mucilage very distinct. Mucilage 
very refractive, sometimes stratified. Cells irregularly scattered. 
The single colonies were generally ellipsoidal or ovoidal in outline, 
averaging about 140-150/x in length, 60-95/x in width. The cells 
were generally comparatively large (6/x diam.) and filled with gas 
vacuoles. The stratification was often very faint, often absent in the 
young colonies. The latter were generally found in groups and were 
often very small. In the younger state the distinction from M. viridis 
is largely one of degree. M. marginata is not so abundant as M.flos- 
aquce. 
Loc. Perithpan-pokuna near Isurumunija-temple at Anuradha¬ 
poora, Oct. 3rd; rock pool connected with Kalawewa-tank, Sept. 
29th (rare); small shallow bay of Nuwarawewa near Anuradhapoora, 
Oct. 2nd (rare). 
MICROCYSTIS VIRIDIS (A. Br.) Lemm. (see (5)) 
Colonies round or rectangular in outline, consisting of a group 
of partial colonies surrounded by a common sheath. Cells 3-7/x diam., 
spherical, with pseudo vacuoles. In both this and the previous species 
the mucilage is highly refractive, clearly defined at the margin and the 
cells are extremely variable in their grouping (see (l)). 
Loc. Small shallow bay of Nuwarawewa near Anuradhapoora, 
Oct. 2nd. 
MICROCYSTIS HOLSATICA Lemm. (see (5)) 
Colonies spherical or ellipsoidal, clathrate, margin of colonial 
mucilage clearly defined. Cells about i/x diam., spherical or sub- 
spherical, without pseudovacuoles. The lacunae were irregular in form 
and variable in size, often about ten times the diameter of the cell. 
Phyt. xxii. 2. 
5 
