A revision of the ammonites from Maastricht and adjacent parts of Limburg and Liège based on the BINKHORST Collection in the Museum für Naturkunde, Berlin, the collections of the Institut Royal des Sciences naturelles de Belgique, Brussels, (including material described by A. DE GROSSOUVRE in 1908) and the Natuurhistorisch Museum, Maastricht, revealed the following sequence of faunas. The youngest Campanian ammonite from the Vaals Formation is a specimen of Hopliloplacenticeras marroti (COQUAND, 1859) from Vijlen, Cotessen (Zuid-Limburg, The Netherlands); this is a typical lower Upper Campanian species. The Zeven Wegen Chalk yields Baculites at several localities and upper Upper Campanian Hopliloplacenticeras coesfeldiense (SCHLUETER, 1867) and Trachyscaphites spiniger (SCHLUETER, 1872) at Vijlenerbosch (Zuid-Limburg, The Netherlands): these are Bostrychoceras polyplocum Zone species. An unspecified horizon within the Gulpen Formation of Schneeberg, north of Vaals yields the lower Lower Maastrichtian Acanthoscaphites tridens (KNER, 1848); the same species occurs at Vaals. No ammonites were seen from the Beutenaken Chalk, but the Vijlen Chalk yields phosphatised and unphosphatised Baculites at a number of localities, Hoploscaphites tenuistriatus (KNER, 1848) at Mesch (Zuid-Limburg, The Netherlands), and there is a record of Pachydiscus sp. from Hallembaye, Liège. No ammonites were seen from the Lixhe or Lanaye Chalks. The base of the Valkenburg Chalk yields phosphatised Baculites anceps LAMARCK, 1822, and phosphatised Baculites sp. at the Blankenberg Quarry, Cadier en Keer (Zuid-Limburg, The Netherlands). No ammonites were seen from the Gronsveld, Schiepersberg or Emael Chalks. Ammonites known to be from the Nekum Chalk, mostly from the environs of Maastricht, are Anapachydiscus fresvillensis (SEUNES, 1890). Diplomoceras cylindraceum (DEFRANCE, 1816), Baculites vertebralis LAMARCK, 1801, B. anceps LAMARCK, 1822 and Hoploscaphites constrictus (J. SOWERBY. 1817). There are two records of Sphenodiscus binkhorsti BOEHM, 1898 from this unit. Ammonites known to be from the Meerssen Chalk are Nostoceras sp., Diplomoceras cylindraceum (DEFRANCE, 1816), Baculites vertebralis LAMARCK, 1801, B. anceps LAMARCK, 1822 and Hoploscaphites constrictus (J. SOWERBY, 1817). The upper part of the Meerssen Chalk only yields frequent Sphenodiscus binkhorsti BOEHM, 1898 and the crassus form of Hoploscaphites constrictus. A single specimen of Eubaculites lyelli (d'ORBIGNY, 1847) from Maastricht is from either the Nekum of the Meerssen Chalk. Ammonites from the upper part of the "Calcaire de Kunraed" are Saghalinites sp., Pachydiscus (Pachydiscus) gollevillensis (d'ORBIGNY, 1850), P. (P.) cf. jacquoti SEUNES, 1890, Anapachydiscus fresvillensis (SEUNES, 1890), Glyptoxoceras cf. subcompressum (FORBES, 1846), G. cf. circulare SHIMIZU, 1935, G. sp., Diplomoceras cylindraceum (DEFRANCE, 1816), Baculites vertebralis LAMARCK, 1801, which is common, B. anceps LAMARCK, 1822, Hoploscaphites constrictus (J. SOWERBY, 1817), H. felderi sp. nov., H. pungens (BINKHORST, 1861). Acanthoscaphites verneuilianus (d'ORBIGNY, 1841) and Acanthoscaphites sp. These ammonites records are in accord with recent work on the belemnites of the region (SCHULZ and SCHMID, 1983) that has shown the Zeven Wegen to Beutenaken Chalk to be Lower Maastrichtian, the Vijlen to lower Meerssen Chalk to be Upper Maastrichtian, Belemnitella junior Zone and only the upper part of the Meerssen Chalk to be Upper Maastrichtian, Belemnella casimirovensis Zone. The upper part of the "Calcaire de Kunraed" yields Upper Maastrichtian ammonites that show it to be older than the upper part of the Meerssen Chalk, compatible with microfaunal work by VILLAIN (1977) and the presence of belemnites of the Belemnitella junior Zone but not of the Belemnella casimirovensis Zone. Also included in this work is a revision of the classic Maastrichtian ammonite Pachydiscus colligatus BINKHORST, 1861. The syntypes are shown to belong to two genera, Pachydiscus and Anapachydiscus, and to at least four species. The lectotype, herein designated in accordance with customary useage, is shown to be from the Upper Campanian of Jauche (Brabant, Belgium)
