Measurements on Globigerinoides trilobus trilobus (Reuss) suggest that rate of chamber expansion is a useful criterion of stratigraphic position in the Awamoan-Altonian Stages (New Zealand), and Catapsydrax stainforthi — Globigerinatella insueta Zones (Trinidad), that may avoid current difficulties in the use of G. t. trilobus and G. bisphericus as homotaxial markers. Angle of attachment of the final chamber, extent to which this chamber envelops the rest of the test and shape of the primary aperture show local trends but are less useful for inter-regional correlation within the interval studied.