Decapod crustaceans from the Mesozoic of Madagascar have been studied by a number of authors during the last century. One of the largest sets of specimens was collected by the French General Maurice Collignon between 1930 and 1950; this was subsequently studied by Secrétan (1964) who described numerous species of macrurans, brachyurans, and axiideans. These crustaceans originate from the Upper Jurassic and the Upper Cretaceous of the Mahajanga Basin (NW Madagascar) and, especially, from the Morondava Basin (central-SW Madagascar). The purpose of the present study is twofold: to furnish an update of the stratigraphy and geology of the studied areas and, above all, to revise the Secrétan's species, employing current systematic nomenclature, supplying for each detailed geographic and stratigraphic data since such were either cursory or incomplete in previous papers. The present revision considers 13 species recorded by Secrétan as valid, namely: Enoploclytia collignoni Secrétan, 1964, Eryma granuliferum Secrétan, 1964, Pustulina spinulata (Secrétan, 1964) (all Erymidae Van Straelen, 1925); Hoploparia collignoni (Van Straelen, 1949), H. pusilla Secrétan, 1964 (both Nephropidae Dana, 1852 sensu Tshudy & Babcock 1997); Ctenocheles madagascariensis Secrétan, 1964 (Ctenochelidae Manning & Felder, 1991); Schlueteria menabensis Secrétan, 1964 (Axiidae Huxley, 1879); Linuparus bererensis Secrétan, 1964 (Palinuridae Latreille, 1802); Dromiopsis pulchella Secrétan, 1964 (Dynomenidae Ortmann, 1892); Caloxanthus simplex (Secrétan, 1964) (Etyidae Guinot & Tavares, 2001); “Xanthosia” robertsi Secrétan, 1982 (nomen novum pro Xanthosia elegans Secrétan, 1964, non Roberts, 1962), Titanocarcinus mamillatus Secrétan, 1964 (both Xanthoidea incertae sedis); and Secretanella arcuata (Secrétan, 1964) (indeterminate family). The three species described by Secrétan (1964) as belonging to the raninid genus Notopocorystes McCoy, 1849, N. bituberculatus, N. australis and N. denisae will be revised in a forthcoming paper. Our comparative studies have also revealed a number of synonymous taxa, as follows: Eryma granuliferum Secrétan, 1964 (junior synonym: E. madagascariensis Secrétan, 1964); Linuparus bererensis Secrétan, 1964 (junior synonym: L. bererensis multispinosus Secrétan, 1964); Hoploparia collignoni (Van Straelen, 1949) (junior synonym: H. intermedia Secrétan, 1964 and H. sculpta Secrétan, 1964); Schlueteria menabensis Secrétan, 1964 (junior synonym: S. tuberculosa Secrétan, 1964). Lastly, we hav