The terms 'Eutheria and 'Placental' do not mean quite the same thing. A few early eutherians in the Lower Cretaceous were not placentals. Eomaia is the earliest example.
All living Eutherians are placental mammals. This means that a Eutherian fetus is fed during gestation by a placenta. The offspring of Eutherians are carried in the mother's uterus until fully developed.