West
    Yunnan was attributed to the Shan-Thai Terrane or to the Sibumasu Terrane by
    some geologists (Burrett et al., 1 990;Fortey and Cocks, 1998). Alternatively
    by other geolo-gists it has been divided into eastern and western parts along
    the Lanchangjiang Fault:assigned respectively to the Indo-China and Sibumasu
    terranes. Ordovician strata are exposed intermittently in eastern West Yunnan, the
    Lower to Middle Ordovician rock sequence being particularly well exposed in
    Xiangyang village near Dali, where it is represented in ascending order by the
    Haidong, Hsiangyang, and Tongchang formations. The Haidong Formation reaches
    more than 384 min thickness, of massive to thick-bedded fine sandstone and quartzite.
    It is unfossiliferous but the correlative context shows it to be basal
    Tremadocian to Middle Arenigian in age. The fauna is rich in brachiopods, especially
    Ectenoglossa daliensis sp.nov., Monor-this intercalase sp.nov., and
    Nocturnellia oriental is sp.nov., and in bivalves such as Fasciculodonta
    impressa Fan et al. and Yunnanoredonia laevis Fan et al. A strophomenoid fauna
    occurs only at the base of this interval, yielding abundant Murinella
    xiangyangensis sp.nov.and a few other brachiopods, such as Tritoechiasp.and
    Fenxiangellasp.