Factor analysis, discriminant functions analysis, and the Mahalanobis D 2 distance function are applied to a case of convergence between the two Upper Pennsylvanian gastropod species Worthenia tabulata (Conrad) and Glabrocingulum (Ananias) welleri (Newell). Selenizone width shows a high degree of ontogenetic independence from other characters and is the most reliable means of differentiating the two species. A parallel trend for increase in whorl height is demonstrated, and inconsistencies in the trend in the phylogeny of G. (A.) welleri are shown. A tentative pattern of convergence is presented which shows relative rates of morphological change in the two species, the direction of the convergent evolution, and relative degree of convergence over successive stratigraphic horizons.