Systematic changes with time in the coiling direction of the planktonic fora-miniferal genus Pulleniatina provide useful datum levels for interregional correlation of Pliocene-Quaternary marine sediments. The pattern of coiling-direction changes was concordant throughout the world oceans from about 6 to 3.5 m.y. B.P. From about 3.5 to 2.3 m.y. B.P., this genus disappeared from the Atlantic and its adjacent seas. After the re-establishment of Pulleniatina in the greater Atlantic about 2.3 m.y. ago, the Atlantic coiling patterns were no longer correlative with the Indo-Pacific patterns. I consider the primary cause of the discordant coiling-direction patterns between the Atlantic and Indo-Pacific Oceans to be the severance of the tropical marine connection across Central America about 3.5 m.y. ago and the subsequent development of two independent faunal provinces.

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