Distribution: Texas; West Indies to Brazil. Size: 28 mm (1½ in). Description: Color white; shape trigonal-oval; sculpture similar to that of A. brasiliana but radial ribs thinner, beads not as elongate, and numerous con- centric ribs in area between radial ribs; pallial line simple; hinge line short with many comblike teeth becoming smaller toward the center. Habitat: Commonly found in beach drift south of St. Joseph Island. Found on entire Texas coast from shoreline to a depth of about 75 m (246 ft). Remarks: Resembles A. brasiliana when fully mature. Common name listed as "Chemnitz's ark." Turgeon et al. (1998) suggest "Chemnitz's triangular ark" to describe its shape. See Odé (1978b); Mikkelsen and Bieler (2008). Synonym: Anadara chemnitzii (Philippi, 1851).

Rounded trigonal, left valve slightly larger, inflated, solid, white with thin light brown periostracum, with ca. 25 squared radial ribs crossed by barlike beads, no byssal gape; interior white, margin coarsely denticulate, cardinal area trigonal, hinge line straight, teeth dense subumbonally. Florida, West Indies, Gulf of Mexico, Caribbean Central America, South America (to Uruguay). Length 30 mm. Compare Scapharca brasiliana which is thinner shelled with more radial ribs.