New species of Early Ordovician bivalves and rostroconchs from the northwestern Argentina basin are described. Bivalves include the following species: Cienagomya bidentata new genus and species, Goniophorina tenuicostata, Lipanella purmamarcensis new genus and species, Ucumaropsis lermaensis new genus and species, and Coxiconchia babini new species. Among rostroconchs, Ribeiria pojetai new species is recognized. Cienagomya bidentata (late Tremadoc–early Arenig) may represent a phylogenetic link between the families Intihuarellidae and Cycloconchidae. The new family Lipanellidae is erected to include Lipanella n. gen. Recognition of Ucumaropsis n. gen. in the early Arenig attests to the important radiation of the Anomalodesmata in northwestern Argentina.