Study of DSDP sites and piston cores from the Northern Atlantic Ocean provided new knowledge of the range and distribution of the Globorotalia crassaformis plexus. The following subspecies are differentiated: Globorotalia crassaformis crassaformis, G. crassaformis ronda, G. crassaformis hessi, G. crassaformis viola, and G. crassaformis imbricata and are described and illustrated. A similar sequence of FADs and LADs of the plexus was recorded in different climatic realms. G. crassaformis crassaformis appeared at 5.06 Ma in the subtropical region and at 4.62 Ma in the boreal realm. It was then followed by other subspecies in a specific succession. At all sites G. puncticulata appeared slightly later than the earliest members of G. crassaformis ss. Its first occurrence data range from 4.88 to 4.54 Ma in different realms. The stratigraphic significance of the plexus is considerably greater than has formerly been recognized and it may be recommended for wider use in the Pliocene-Quaternary zonations.