The relationships of some important species related to the genera Paracosta, Loxoconcha, Leguminocythereis and Uroleberis from the Paleogene deposits of Egypt have been revised. The achieved results are encouraging toward producing a monograph on the Paleogene ostracods of Egypt.Detailed study of these genera revealed the distinction of a phylogenetic series within the genus Paracosta (Paracosta palaeomokattamensis-Paracosta mokattamensis). Moreover, the studied Loxoconcha species that were thought to represent a phylogenetic series by some authors assumed in this study to represent two species inherited from one ancestor, while the third from another ancestor. On the other hand, the studied Middle Eocene Leguminocythereis species are an example of the so-called environmentally cued polymorphism. Whereas, the studied species previously referred to the genus Uroleberis assumed in this, study to represent the genera Uroleberis and Foveoleberis. Overall, Paracosta mokattamensis praemokattamensis seems to be a good stratigraphic indicator of the Lower/Middle Eocene boundary.