Comparison of the primary aperture ofGlobigerinoidesfrom the lower Miocene of Trinidad and New Zealand

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Abstract
Apertural dimensions of Globigerinoides from the lower Miocene Globorotalia kugleri — Globigerinatella insueta zones of Trinidad and Otaian-Altonian stages of New Zealand are closely similar at equivalent stratigraphic levels. Nomenclatural and stratigraphical confusion which affects the application of Bandy’s “Globigerinoides trilobus datum” is possibly resolvable by restricting G. trilobus trilobus (Reuss) to low-apertured populations. In both regions these can first be distinguished about the level at which Globorotalia scitula praescitula Blow appears (C. stainforthi zone; Hutchinsonian-Awamoan stages). So defined, the advent of G. trilobus trilobus may itself provide a useful homotaxial datum which should be distinguished from the initial appearance of the Globigerinoides trilobus group in the lower Miocene as the high-apertured G. trilobus altiaperturus Bolli (G. kugleri zone; Otaian stage).