Twelve characters on the dorsal valve of Neochonetes granulifer (Owen) were measured and subjected to multivariate analysis of variance. The specimens were collected from 26 localities which represent seven different geologic units ranging in age from late Desmoinesian to late Wolfcampian. The statistical procedures successfully resolved geographic variation and evolutionary change. They also showed the relations between many measured characters as they evolved. Three-space graphs were constructed, using as axes three discriminant functions which explained 95-98% of the variation. Means projected onto discriminant functions and discriminant functions alone were plotted on these graphs for ease in visualizing relative similarities between sampled populations and influence f the measured characters on the sampled populations. Geographic variation within any one sampled stratigraphic unit was small. The statistical method tended to separate limestone assemblages from shale assemblages. This finding raised the question of whether a population as a continuum or two ecologically controlled populations of the same species were represented by the samples. If, on further investigation the latter is found to be correct, the statistical method employed will have been shown to be a very useful tool for discerning morphologically similar but ecologically different populations of the same species.

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