Three major zones are recognized (Zones A, B, and C) in the molluscan faunas listed and described in this paper. The fossils were collected from deposits of middle and upper Eocene age in the El Carmen district, Department of Bolivar, Colombia.
The Zone A fauna, referred to the middle Eocene, contains species closely related to some from the middle Eocene of Peru and to two others originally described from the middle Eocene of California.
The Zone B fauna contains several species identical and a number closely related to those described by Olsson from the Talara formation of Peru. Olsson considers the Talara fauna equivalent to the lower Jackson of southern United States and to the Bartonian of Europe.
The Zone C fauna is the largest and the best preserved. It contains species described by Olsson from the Saman formation and the Chira shales of Peru, which deposits he considers upper Eocene and lower Oligocene. These deposits have too much in common to warrant such a separation and should be considered as one major zone, which is equivalent to Zone C of Colombia. Several species in Zone C are common to the Jackson of southern United States. These deposits are tentatively correlated with those of the upper Jackson.
Nine species of corals occur in the upper Eoccne faunas collected in the El Carmen district. These include the following genera: Antilla, Antillophyllia (?), Coeloria, Favia, Flabellum, Goniopora, Podasteria, Turbinolia, four of which are typically reef-forming or shallow-water corals. Turbinolia olssoni Wells was described from the Mancora formation, Olsson’s middle Oligocene of Peru.
A large number of the molluscan genera recognized in the Eocene of western South America have not been found in any other general Eocene province; a considerable number of these are found in later Tertiary deposits, and some are living today, not only in the South American provinces but also in other areas. This seems to indicate that the areas of deposition in western South America were fairly well isolated during Eocene time and that evolution was taking place there independently. Such conditions account for the sudden appearance of many new genera in the later Tertiary deposits throughout the world.