Abstract: Very abundant ostracod. lamellibranch, brachiopod and trilobite fossils have been found in the strata assigned by predeccessors to the Silurian-Devonian "Lugou Formation" and Upper Silurian "Gurban River Formation" in the Snhu River area, Inner Mongolia. The ostracods are represented by Brevibolbine, Ctenentoma, Ceratobolbina, Higganobolbina, Sibiriobolbina and Sigrnobolbina, including 12 genera and 11 speeied （1 new genus and 4 new species）. The above-mentioned fossils are mainly distributed in Mid-Late Ordovician strata in Estonia and Lithuania of the U.S.S.R., Germany and Czechoslovakia of Central Europe and Norway and Sweden of Northern Europe. This ostraeod fossil assemblage was for the first time discovered in the Greater Khingan Mountians region of China. It is of very important significance for the study of China’s Ordovician biogeographical provinces and the international stratigraphieal correlation.