Conodont faunas Ordovician boundary from the Middle and Upper interval are recorded from Ln 50 well in the Lunnan exploration area, north- western Taklimakan Desert, Xinjiang, China. The fauna includes Pygodus anserinus, P. serra, P. xinjiangensis, Ansella jemtlandica, Cornuodus longibasis , Periodon aculeatus , Protopanderodus calceatus, P. cooperi, P. varicostatus, Scabbar- della altipes , Spinodus spinatus , and Cahabag- nathus sweeti, etc. Three conodont zones can be recognized. In descending order they are the Pygodus anserinus , P. serra and P. xinjiangen- sis zones. The Middle and Upper Ordovician boundary is just above the base of Pygodus anseri- nus Zone. In this paper, particular attention is paid to Pygodus xinjiangensis, the evolution of Pygo- dus, and the differences between these three species. Because species of P.ygodus are of extraordi- nary importance for global correlation, the results of present study, which have clarified some taxo- nomic problems within this genus, are of interna- tional significance.
