About seventy ostracod species are present in the upper part of the Hanonet Formation (Upper Eifelian) and in the base of the "Trois-Fontaines" Formation (Lower Givetian) of the "La Couvinoise" quarry at Couvin (southern border of Dinant Basin, Belgium). The ostracods belong to the "Eifeler Okotyp" and four associations are recognized which characterize successively a quiet open marine environment on the outer ramp (ecozone III), a shallow marine environment with increasing of water turbulence on the mid- and inner ramps (ecozone II), an open lagoonal environment on the upper part of the inner ramp (ecozone I) and a restricted lagoonal environment on the platform (ecozone 0). This sequence is the same as in the Resteigne quarry (50 km E of Couvin) studied by CASIER & PREAT (1990 & 1991) and is closely related to environmental variations. The principal ecological factors controlling the composition of the ostracod fauna are water movement in the Hanonet Formation (Eifelian), and water movement and salinity in the Trois- Fontaines Formation (Givetian). Two new species are erected: Condracypris? covinumensis n. sp. et Microcheilinella? hanonetensis n. sp.