The succession of the mid-Bashkirian ammonoids Cancelloceras and Gastrioceras in North China

Abstract The ammonoid genera Cancelloceras and Gastrioceras are important index fossils for the subdivision of mid-Bashkirian strata; both are represented by species in the Qilian Mountain region of Gansu and Ningxia (North China). In the Xiaoyuchuan section, four successive ammonoid assemblages were recorded, in ascending order with Cancelloceras pachygyrum, Cancelloceras zhoungweiense, Gastrioceras stenumbilicatum and Gastrioceras wongi. These species are revised here, together with a description of the new species Homoceratoides wangchengi Korn and Wang, n. sp.