This paper deals with characteristics of the conchostracan assemblage and describes some new species of fossil conchostracan collected from the bottom of the Ermayin Formation near Changjiayan of Wupu County, Shaanxi in 1983.After studying and comparing this conchostracan assemblage, the writer here suggests that (1) this assemblage is characterized by leading members of Protomonocarina and Euestheria, rare but very important members of Xiangxiella and many members of Palaeolimnadiopsis and Diaplexa; (2) this fossil fauna has a close relation to that of the Heshanggou Formation, but itis more different from that of the Tongchuan Formation.It is of great significance to compare the regional stratigraphical sequence, because the strata containing this conchostracan fauna are more stable in North China.This fossil fauna may be called the Protomonocarina-Euesteria fauna, representing the conchostracan fauna of early Middle Triassic in North China and resembling the Xiangxiella fauna in South China.