W.  Michaelsen, ?Zur kenntnis der Didemniden?, Abhande. Natur. wis. ver. Hamburg, vol. 21, no. 1, pp. 1-44, 1919.

W.  Michaelsen, ?Ascidie Ptychobranchiae un Diktyobranchiae des Roten Meeres?, Denkschriften der Akademie der Wissenchaften, Wien, vol. 95, pp. 1-120, 1919.

R.  Hartmeyer, ?Ascidien. In: Results of Dr. E. Mjoberg?s Swedish scientific expedition in Australia 1910-13?, Koninklijke Svenska Vetenskapsakad Akademie der Handlingar, vol. 60, pp. 1-150, 1919.