Family Cyrenidae

Shell size to 25 mm; shell trigonal, with rounded ventral and pointed posterior margins. Sculpture restricted to irregular growth lines. Color whitish with purple or pinkish-purple tints. Internally mostly white, but sometimes purple or white with purple margin. This is an estuaribe species that sometimes washes onto the passes around the barrier islands of Southwest Florida. Polymesoda maritima (d’Orbigny, 1853) is a synonym. Photos by Patricia A. Starkey.

This species may grow to 50 mm (about 2 inches.) Its shell is oval, with a sculpture of fine commarginal ("concentric"), regularly spaced ridges. The shell color is brown. It differs from the Southern Marsh Clam, Polymesoda floridana, by having a more rounded shell with truncated posterior end (left end of leftmost views on photo). This is a truly brackish water species, inhabiting the upper reaches of local estuaries (the shell illustrated was collected in the Caloosahatchee River estuary.) Photos by Patricia A. Starkey.