Ostracods of the Mojcza Limestone

82 ostracod species, belonging to 51 genera, included in three orders (Beyrichiocopa, Platycopa and Podocopa) from the Ordovician Mojcza Limestone at its type locality at Mojcza (Holy Cross Mountains) are described, 6 genera and 39 species being new. Only a few species are shared by the Holy Cross Mts and Baltoscandian ostracod faunas. Most of genera from Mojcza are known from Baltoscandia, some occur also in Ibero-Armorica, the British Isles and Bohemia. Phosphatized ostracod valves occur in Mojcza in carbonate sediments probably deposited in a stable environment with very slow sedimentation rate. Diversity of the assemblages is generally high and rather stable in time especially in the Middle Ordovician. It is somewhat lower in the basal part of the sequence, gradually increases during the Llanvirn and Landeilo, then strongly decreases in the early Caradoc while increasing again in the middle Caradoc. Biometrical population studies of morphologic evolution demonstrated that larger elements of shell ornamentation (such as crests or spines) were subject to evolutionary changes while the microomamentation remained unchanged; microornamen ation is stable also in the ontogeny. The Mojczella lineage is the best example of smooth acceleration in ontogenetic expression of the junction of crest C l and C3, which originally were separated throughout the ontogeny. Probably environmentally controlled variation in size of carapaces in time has been shown for several species. The pore canals in walls of the Ordovician ostracods and special morphological features, which are believed to have functioned for buoyancy control, are described. Morphology of the tubulous velar structure is described.