Five planktonic foraminiferal zones can be recognized in the late Miocene to middle Pliocene of Long, Car Nicobar, and Chowra Islands, Bay of Bengal. The early Pliocene marker species Globorotalia margaritae first makes its appearance slightly above the horizon marked by the first evolutionary development of Sphaeroidinella dehiscens from its immediate ancestor Sphaeroidinellopsis subdehiscens (which marks the Zone N. 18-N. 19 boundary of Banner and Blow). The first evolutionary appearance of Sphaeroidinella is a valid datum in tropical regions and marks the Miocene-Pliocene boundary. This level is stratigraphically much lower than the “S. dehiscens datum” described by Bandy in the Philippines. The important temperate Pliocene-Pleistocene forms, Globorotalia inflata, G. puncficufato, and G. crassoformis ore absent, presumably because of the tropical conditions in the Bay of Bengal.