FRESHWATER PLANKTON ALCjLE FROM CEYLON 
141 
by the demonstration of the presence of similar septa in these small 
species if appropriate stains be used (see Schmid, Archiv f. Protist. 
xliii.). 
S. princeps W. & G. S. West. Loc. 30, 38. Distr. Eur., 
Afr., Java, Ceylon. 
S. ten uiss lma Kuetz. The only species in which the coils of the 
spiral are so close as practically to rest one upon the other. Our 
specimens occurred generally as separate trichomes; only in a few 
cases were two or more laterally adherent. Trichomes 1—2 p in 
width ; coils 3*5 pin width ; the} ? sometimes show signs of secondary 
spiral coiling. Previous records have been chiefly from brackish 
water, as in this case. Loc. 1. Distr. Eur., Afr., W. Indies. 
Oscillatoria Vaucher. 
Represented by species that are equally abundant in the north 
temperate fresh waters, but some perhaps tend to warm water. 
0. princeps Vaucher. This, which is at first benthic, growing in 
mats, was found as solitary trichomes, easily recognised by their 
large size, flattened segments, and very characteristic apices. Al¬ 
though frequently recorded for temperate regions, a number of these 
records are for warm water. Diam. fil. 27 p. Length of seg¬ 
ments 3 p. Loc. 32, 33, 34. Distr. General (inch Ceylon). 
0. tenuis Ag. As the free-floating form : O. natans Kuetz. 
O. tenuis var. natans (Kuetz.) Gomont. Largely in heleoplankton. 
Loc. 2, 13, 24, 25, 30, 32, 35, 36, 38, 39. Distr. General (inch 
Ceylon). 
0. limosa Ag. Mostly in floating masses. Loc. 9, 25, 35, 38, 
40. Distr. General (inch Ceylon). 
0. cortiana Menegh. This has been found in warm water 
in both N. America and Central Europe and also in the plankton of 
Tanganyika by G. S. West. It is therefore somewhat surprising 
that a form of it should have been recorded by W. & G. S. West 
from Clear Lake, Cape Koyds, in the Antarctic ; but the specimens 
from the latter locality had cells appreciably shorter than long, and 
may therefore have been distinct. In the Ceylon material the 
dimensions were normal: trichomes 5‘5-8 p in diameter, segments 
5*5-8 p long. Loc. 13. Distr. N. Temp. 
O. Agardhii Gomont. Loc. 8. Distr. N. Temp. 
0. rubescens DC. Loc. 41. Distr. N. Temp. 
O. cruenta Grunow. Floating in littoral region. Loc. 37. 
Distr. N. Temp. 
O. proboscidea Gomont. Floating in littoral region. This 
well-defined species has been found as far north as Alaska. Loc. 13, 
33. Distr. Eur., N. and Central Amer. 
O. Mougeotii Kuetz. Loc. 13, 42. Distr. N. Temp. 
O. amphibia Ag. Loc. 35. Distr. General. 
O. ciilorina Kuetz. Loc. 26, 33, 35, 40, 44, 45, 48. Distr. 
General. 
O. margaritifera Kuetz. A marine species, found in Trinco- 
malie Harbour. Loc. 46. Distr. N. Temp. 
O. subtillissima Kuetz. The validity of this species, in view of 
its few definite characters, seems very questionable. It is, however, 
