This volume, 9C, in two parts, covers the Brachyura. With the publication of the ninth volume in the Treatise on Zoology: The Crustacea, we departed from the sequence one would normally expect. Some crustacean groups, mainly comprising the Decapoda, never had a French version produced, and the organization and production of these “new” chapters began independently from the preparation of the other chapters and volumes. Originally envisioned to encompass volume 9 of the series, it quickly became evident that the depth of material for such a volume must involve the printing of separate fascicles. The new chapters have now been completed, and the production of volume 9 was started while volumes 3 through 8 were (and in part still are) in preparation; with this vol. 9C-I & II this volume 9 is now concluded; vols. 1-5 have also been published and vols. 6-8 are being prepared.