Article: Ordovician trilobites from Chedao, Gansu Province, north-west China
Zhou Zhiyi and W. T. Dean
Two trilobite assemblages of middle Llandeilo to basal Caradoc and of Caradoc age are described from the type section of the Chedao Formation at Chedao, Huanxian County, Gansu Province, north-west China. They include twenty-nine taxa, of which five are new species: Phorocephala quadrata, Peraspis obscura, Microparia (Quadrapyge) chedaoensis, Ischyrophyma? zhiqiangi, and Hammatocnemis obsoletus. The composition of both assemblages approaches that of the Nileid Association and suggests that the Huanxian area formed part of the western slope of the North China carbonate platform. The presence of genera such as Peraspis, Lyrapyge, and Cyphoniscm indicates that some genera once thought to have a short stratigraphic range persisted much longer when appropriate environments were available.