The foraminiferal family, Miogypsinidae, contains evolutionary series, the successive units (species) of which are common to the Louisiana Gulf Coast, Florida, the Caribbean region, and the Mediterranean region. It is suggested that the miogypsinids had a monophyletic origin and that dispersal of some of the evolving groups during the Oligocene and the Miocene was a rapid process. Stratigraphic relationships between miogypsinid species and planktonic Foraminifera in the Gulf Coast offer the key to world-wide correlations and proper use of some of the European terminology.

Oligocene sediments on the western side of the Atlantic contain the probable Rotalia ancestors of the Miogypsinidae, which show only slight differences from widely distributed primitive Miogypsinidae. Chattian beds in both the Old and the New World contain the primitive Miogypsina complanata Schlumberger, while M. bermudezi Drooger, M. thalmanni Drooger and M. panamensis (Cushman) are late Oligocene species restricted to the western hemisphere. M. gunteri Cole and M. tani Drooger are found in the Aquitanian on both sides of the Atlantic. Burdigalian beds are marked by M. irregularis (Michelotti) and M. intermedia Drooger both in America and in the Western Mediterranean area. The American species, M. bronnimanni Drogger, is thought to be yet another Burdigalian-Helvetian representative of the family. M. cushmani Vaughan occurs in Helvetian sediments on both sides of the Atlantic, but M. mexicana Nuttall seems to have been confined to the Helvetian of the western side. M. mexicana was the most advanced miogypsinid in the Gulf Coast and the last member of the family to become extinct here. Both nepionic acceleration and centripetal trends are repeatedly confirmed by the Gulf Coast data.

Further study is needed on planktonic Foraminifera, but at present a late Helvetian age is logical for the ranges of Globigerinatella insueta Cushman and Stainforth, Globigerinoides bispherica Todd, and Globorotalia praemenardii Cushman and Stainforth. Orbulina and Globorotalia menardii (d'Orbigny) seem to have appeared contemporaneously in the Gulf Coast records; the beginning of Orbulina in Europe coincides with the Helvetian-Tortonian boundary, and the range of Globorotalia fohsi Cushman and Ellisor is mainly Tortonian.

It is apparent that this new faunal evidence affords a better understanding of time relationships within the Gulf Coast, which can be extended to areas of tropical America. These fossils indicate that Suwannee limestone which is exposed at numerous Florida localities and fossiliferous carbonate rocks to which the name has also been applied in various Florida wells should be correlated in part with the Chickasawhay formation of Mississippi and in part with the subsurface Anahuac formation and the lower Fleming of Texas and Louisiana. The Tampa limestone of Florida is correlated with the lower middle Fleming. Some of the faunal zones of the Gulf Coast subsurface, such as the well known Heterostegina zone, are considered to be time-transgressive units.