FRESHWATER PLANKTON ALGLE FROM CETLOJG 
111 
In the following account, only the Cyanophyccce and ChJoro- 
pliycece (excluding Heterokontce , but including Akontce') are described. 
The very numerous Diatoms of European fresh waters appear to be 
rare, whilst numerous tycholimnetic forms occur in some of the 
tubes. The Heterokontce were practically absent. A rich zoo¬ 
plankton, mostly Crustacea, also occurs in some localities, but it was 
not investigated. The character of the material and the limitation of 
the investigation to certain classes of organisms of the phytoplankton 
precludes any account of the plankton as an association. On the 
other hand, the material has been dealt with from a systematic point 
of view. Where ecological topics have been touched upon, it has 
been with reference to individual species or other systematic groups. 
Fifty genera, including 138 species, are recorded : of these, seventeen 
genera, including 50 species, belong to Cyctnophycece , and 33, in¬ 
cluding 85 species, to Chloropliyceas. The actual relative propor¬ 
tions in number of species of each of the main groups in the habitats 
represented is, at the season at which the collections were made, 
probably something like the proportion shown by the following lists, 
since although a number of doubtful forms are not listed, these were 
distributed throughout the various families, and mostly consisted of 
rare forms, of which specimens were insufficient in number or un¬ 
suitable for identification. The proportion in number of species 
given above for Cycinopliycece and Chlorophycece is however quite 
unlike the proportion in number of individuals ; and there is no doubt 
that, as in the terrestrial algal flora (see Fritsch), the former group 
is much the more important component. 
Four new species were met with. The two new species of 
Microcystis and Dimorphococcus Fritschii , sp. n., are described else¬ 
where. Thirty-six species recorded here have ‘not previously been 
found in Ceylon ; a large number of the latter, however, are not 
uncommon in the tropics. Many of the Cingalese species have not 
only been found in other parts of the Indo-Malayan region, but a 
high percentage have been frequently recorded from Europe. 
In order to show the geographical significance of the following 
lists, reference is given to the previously recorded geographical distri¬ 
bution of each species. These records, although no doubt incomplete, 
indicate a very wide range of localities for many of our t} f pes. The 
fact that several tropical species also occur in the polar regions is by 
no means fully explained. It is well known that the majority of 
organisms of the freshwater plankton have a very wide area of dis¬ 
tribution. Our records should be compared with those of W. and 
G. S. West; these authors did not deal with the limnoplankton, and 
their records contain many species of limited range. On the other 
hand, we have dealt chiefly with the limnoplankton, which is to a 
large extent made up of the same species as occur elsewhere. 
The localities are referred to by numbers, as given in the following 
table:— 
1. Large brackish pond about 3 miles from Hambantota, 10 Sept. 
2. Four small tanks near entrance to Botanical Gardens, Anurad- 
hapoora, 2 Oct. 
3. Small, shallow bay of Nuwarawewa, near Anuradhapoora, 2 Oct. 
