Phacopida from upper Whiterock (Lower Caradoc) horizons in the Las Aguaditas Formation of San Juan Province, Argentina, include the calymenid Platycalymene trapezoidalis (Baldis and Pothe, 1995) and the encrinurids Frencrinuroides edseli new species, Lasaguaditas oweni new genus and species, and Walencrinuroides? new species A. Sulcocalymene Baldis and Pothe, 1995, a purported subgenus of Flexicalymene, is a junior subjective synonym of Platycalymene Shirley, 1936. Platycalymene is now known from Avalonia, Baltica, Laurentia (Scotland), and the Precordillera. Emending the cladistic analysis of Ordovician Encrinurinae by Lesperance and Desbiens (1995), the monophyly and membership of Frencrinuroides and Walencrinuroides are ambiguous. Frencrinuroides edseli is closely related to species from eastern Laurentia. Lasaguaditas new genus is superficially cybelinid-like in some respects but shares several derived characters with the Encrinurinae. All three encrinurinid species in the Las Aguaditas Formation possess two instars in the protaspid period, a general pattern in Ordovician encrinurinid ontogeny.