Ten species of macruran, anomuran, and brachyuran decapod crustaceans, arrayed in eight families, were collected from seven localities in the Jagüel and Roca Formations, west-central Argentina. All of the decapods were collected from the Maastrichtian Jaqüel Formation and a part of the Roca Formation dated as Maastrichtian–Danian. All but one of the taxa, Xanthilites gerthi Glaessner, represent first occurrences in the unit and six had not been described previously from Argentina. Six taxa, Thaumastoplax rocaensis n. sp., Proterocarcinus lophos n. gen. and sp., Lobonotus lobulata n. sp., Glyphithyreus wichmanni n. sp., and Costacopluma australis n. sp. are new. Comparison of the fauna with Cretaceous and Paleogene faunas in Chile, Antarctica, and New Zealand indicates that the Argentinian fauna was strongly influenced by dispersal from lower latitude, Atlantic and Tethyan sources in marked contrast to the high latitude, Pacific affinities of the other faunas. There is no evidence that the Argentinian brachyuran fauna was seriously affected by the K–T extinction event. Seven of the genera from the Roca Formation are known from Cretaceous and Paleogene rocks.