Clark published a paper "On the Spongiae Ciliatae as Infusoria flagellata" in the "Mem.
"More Letters of Charles Darwin" by Charles Darwin
These flagellata seem to have a rather marked tendency to form colonies.
"The Whence and the Whither of Man" by John Mason Tyler
The Whip-swimmers, or Flagellata; 4.
"The History of Creation, Vol. II (of 2)" by Ernst Haeckel