Campanian ammonites from the Annona Chalk near Yancy, Arkansas

Ammonites are abundant in the phosphatic base of the Annona Chalk (Campanian) near Yancy in Hempstead County, Arkansas. The following are described: Pachydiscus (Pachydiscus) sp. (very rare), Placenticeras sp. (very rare), Nostoceras (Nostoceras) pulcher n. sp. (rare), N. (N.) monotuberculatum n. sp. (scarce), N. (N.) plerucostatum n. sp. (frequent), N. (N.) danei (frequent), Didymoceras sp. (rare), Didymoceratoides binodosum n. gen. and sp. (frequent), D. clardyi n. gen. and sp. (rare), Baculites taylorensis Adkins, 1929 (abundant), B. crickmayi Williams, 1930 (common), and Baculites sp. (abundant). The diverse Nostoceras association is typical of Gulf Coast upper Campanian rocks but Didymoceratoides is a Western Interior upper middle Campanian genus. Nostoceras (N.) monotuberculatum n. sp., however, is known from a single specimen from the basal upper Campanian Didymoceras stevensoni zone in Colorado.