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THE TANGANYIKA PROBLEM. 
I have encountered this scum repeatedly on the lake, the 
clear green for miles appearing as if tinged with a fine 
golden dust, the minute particles of which this is composed 
reflecting the bright sunlight, like the crystals of some 
yellow precipitate. 
Upon examination these yellow clouds were found to 
consist of a large infusorian which at first sight looked 
exactly like a peridinium , having the characteristic equatorial 
groove, but on closer scrutiny the whole organism was found 
to be covered with long cilia which projected in lines from 
the pore-like apertures in the plates of the skeleton. But 
for the groove the animal would thus compare with a large 
colpodium. 
Whatever it really is, this organism is a most conspicuous 
object. I have never seen it in any of the other lakes, and 
it appears to be as characteristic of Tanganyika as the rest 
of the members of the Halolimnic group. 
Associated with the above form, and also present in the 
surface scum, there is a large condylostoma , the affinities of 
which are not doubtful ; and besides these two conspicuous 
and characteristic protozoa, there were found about twenty 
recognisable types belonging to those groups which have 
habitually been encountered in the fresh-waters of the 
tropics. 
