Circular, posterior end slightly produced in some individuals, cream to white with bold orange-brown mottlings and velvety brown periostracum, near-smooth with fine radial ribs bearing fine riblets, umbones orthogyrate; interior white stained with brown. North Carolina to Florida, Bahamas, West Indies, Caribbean Central America, South America (to Uruguay). Length 12 mm (to 50 mm). Compare Glycymeris decussata, which is brown mottled and more posteriorly rostrate. Note: Also known as Wavy Bittersweet.

Glycymeris undata (Linnaeus, 1758) Wavy Bittersweet Distribution: North Carolina to Florida, Texas; West Indies; Brazil. Size: 51 mm (2 in). Description: Color of base whitish with irregular bands and splotches of reddish- brown with a velvety, hair-type periostracum, inner surface whitish with exterior coloration sometimes bleeding through in splotches; shape thick, subcircular; sculpture of finely crowded, furrowed radial ribs with fine, concentric threads, giving beaded appearance; slight ridge from umbo to posterior ventral angle; ventral margin crenulate. Habitat: Sandy bottoms at depths from 0 to 51 m (168 ft). In Texas found at the FGB. Remarks: Upper right photograph shows close-up of periostracum fibers growing out of the shell; lower left photograph of fibers not as magnified. See Rehder (1981); Mikkelsen and Bieler (2008).