Abstract: There are a great number of Colacium Ehr. (Euglenaceae, Euglenophyta) in Lake Dong-Hu, Wuhan, from late autumn to early summer in recent years. They have been identified as C. sideropus Skuja 1939 by observation of their morphology and making research on their cytology, especially on the characteristics of their chromatophoras. But some of their characteristics, the colloidal cushion or colloidal stalk, are similar to C. cyclopicola(Gicklh)Bourrelly and C. vesiculosum Ehr. On the other hand, Some phycologists think that the chromatophoras of C. cyclopicola and C. vesiculosum contain the pyrenoid. Therefore, perhaps they (C. sideropus, C. cyclopicola and C. vesiculosum) and actually of the same Species belonging to Colacium Ehr. Our investigation proves that Rosowski’s viewpoint about classification and identification of Golacium Ehr. is rational, i. e.: the colloidal stalk of Colacium Ehr. can not be considered as an important basis for classifing; and it is necessary for the pyrenoids in chromatophoras of Colacium Ehr. to be stained or observed by electron microscope.