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New microstructural observations on the tests of microperforate and medioperforate planktonic foraminifera from the Oligocene are presented and comparisons are made with some Holocene specimens. Two types and two subtypes of wall texture are distinguished: the glutinata-type (in Globigerinita and Tenuitella; with the danvillensis-subtype in Dipsidripella), and the ototara-type (in most Chiloguembelina), with the chipolensis-subtype (in Cassigerinella and some Chiloguembelina). Given also the gross morphological differences between the two major groups (trochospiral versus biserial or enrolled-biserial), these wall textures likely indicate separate evolutionary radiations from different groups of benthic foraminifera and so help define the higher taxonomy of the planktonic foraminifera. Accordingly, the following superfamilies are recognized in the chapters of this work: Globigerinitoidea and Guembelitriodea. Their placement relative to other superfamilies of foraminifera is not yet known.

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