Thin sections and acetate peels of the sediment within, and adhering to the outsides of, tests of Late Eocene echinoids from the southeastern United States have proven to be useful checks on inferences from test morphology concerning substrate preference. Previous characterizations of species' sediment preferences have concentrated primarily on the functional morphology of spatangoids, and relied particularly heavily upon Recent relatives of nonspatangoids. Reassessment of the preferences of spatangoids has led to a few discrepancies between interpretations herein and those of previous workers. In addition, this study attempts a more thorough assessment of functional morphology of nonspatangoid irregular echinoids than has previously been tried.

Carbonate sand-dwelling species from the Ocala Limestone (thin sections are clean grainstones) include Oligopygus, Echinolampas, Rhyncholampas, fibulariids, Durhamella, Neolaganum, Agassizia, Macropneustes, some species of Plagiobrissus and Periarchus, and most species of Eupatagus. All these have been interpreted previously as preferring clean sand. Species that preferred, or at least tolerated, significant carbonate mud in the substrate (thin sections are poorly washed grainstones and packstones) include all the regular echinoids and the irregular echinoids Schizaster, Ditremaster, Brissopsis, Brissopatagus, Amblypygus, Eurhodia, Weisbordella, Wythella, Paraster, some species of Periarchus and Plagiobrissus, and perhaps some species of Eupatagus. The last seven of these have previously been interpreted as sand-dwellers.

In general, species preferring mud-rich sands are found in the upper Ocala of peninsular Florida and in the middle to upper Ocala equivalents in the rest of the Gulf Coast. Sand-dwellers are most often found in the lower Ocala strata of both regions and up into the middle Ocala in Florida. These generalizations are consistent with existing paleoenvironmental models for the region.