ORDOVICIAN TRILOBITES FROM THE DAWANGOU FORMATION, KALPIN, XINJIANG, NORTH-WEST CHINA

Sixteen trilobite taxa are described from the type section of the Dawa ngou Formation (late Arenig-early Llanvirn) at Dawangou, Kahin, north- western Tarim, Xinjiang, north-west China. They include two new genera : the asaphine Mioptychopyge and the pterygometopine Yanhaoia. Evidenc e from the lithofacies and from the composition and taphonomy of the a ssemblages suggests that the fauna lived in a generally calm, upper sl ope environment. More than 80 per cent. of the species are common, or closely allied, to coeval forms in the Yangtze region, indicating a cl ose palaeogeographical relationship between the Tarim and South China blocks during the late early Ordovician. Some genera, such as Birmanit es, Eccoptochile, Ovalocephalus and Pseudocalymene, are typical of Gon dwanan faunas, and it is likely that the Tarim Block formed part of pe ri-Gondwana in the Ordovician.