Although wall structure is the major basis of taxonomic distinction between two lower Miocene species of the arenaceous textularid genusHaeuslerella, it is difficult to use in some samples. As an aid to identification, measures of external morphology ofHaeuslerellain the type sample ofH. deceptaHornibrook are used to compute functions which minimise errors of classification without recourse to analysis of wall structure. Diameter of the proloculus provides a useful discriminator, but, in upper Otaian to Awamoan samples, risk of misclassification can be lowered by applying a linear function of proloculus diameter and test widths.