Language: Dutch with 31-page French summary
Volume 4, Fascicle 2 (pages 229-524) covers the second half of the passeriform birds of Belgian Congo and Ruanda-Urundi (which later became Rwanda and Burundi). A French summary with identification keys is included. Finally, an index to the species treated in volume 4, fascicles 1 and 2 (parts VI and VII in the numbering of the birds) is included.