Prestwoodia delicata (Travassos, 1946) Anderson, 1978, Heterostrongylus heterostrongylus Travassos, 1925 and Didelphostrongylus hayesi Prestwood, 1976 are redescribed on the basis of new collections of specimens from Didelphis marsupialis from North and South America. The three genera are unique to the opossum. Prestwoodia from the nasal sinuses is most similar to Troglostrongylus of Felidae. Heterostrongylus and Didelphostrongylus are similar in size and certain other features such as their six prominent lips and reduced bursae. The dorsal ray in the former, however, consists of a large, rounded lobe whereas in the latter, it is divided into two long branches. Didelphostrongylus is found under the pleura whereas Heterostrongylus is found in the bronchi. ac]19790102