On the Gulf Coast, as in other areas, ostracods have been much used in interpreting paleoenvironments. Such use may be enhanced by study of the ocular structures, including eyespots. Eyespot morphology appears to relate to light levels, which in turn are related to water depths. Thus, a new means of reconstructing water depths may be available.

Eyespots from two species of Echinocythereis from modern sediments along the Gulf Coast were studied using polished sections and electron and light microscopy. The inner surface of an eyespot is undulating and has a central convex portion and posterior concavities, each with a small radius of curvature compared to the convex outer surface. Light is converged most strongly by the central area and is focused in the underlying eye space. Astigmatism occurs as light passes through the areas away from the center, in which case the focus is beyond the eye cavity in the absence of a tapetal layer. Comparison of a modern and an extinct (Eocene) species of Echinocythereis indicates similar morphology and presumably similar functioning. A potential exists for discerning modern morphology as rel ted to water depth and applying such knowledge to fossil forms and their environments.

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