A collection of about 1300 well-preserved ammonoids has been secured from several localities in the Winslow Formation of northwestern Arkansas. Representatives of the genera Eoasianites, Pseudoparalegoceras, Stenopronorites, and Winslowoceras are restudied. The stratigraphic significance of Diaboloceras, Paralegoceras and Winslowoceras are discussed. New species of Wiedeyoceras and Gastrioceras are described. It is concluded that the Winslow Formation is older than typical Atokan and should be classed as late Morrowan.