AbstractThe prolific foraminiferal fauna of the upper Cretaceous Arkadelphia Marl (southwestern Arkansas) is described and illustrated. Previous literature on the Foraminiferida of the Arkadelphia is scattered and confused. All 118 known species from the formation are re-described and numerous taxonomic revisions are made to correct generic assignments in conformity with modern usage. Twenty-four other speciesgroups which have been reported from the Arkadelphia by earlier writers are reviewed and discussed. It is suggested that most of these are erroneously attributed to this horizon. A range chart and a brief discussion of the fauna! zones within the formation are included. The fauna of the Arkadelphia indicates that it may be correlated with the Navarro Formation of Texas, The Monmouth Formation of Maryland, the Navesink and Mount Laurel formations of New Jersey and the Maestrichtian group of the Senonian stage of the European Cretaceous.