This particular shell apparently falls under the category of "Venus Clams".
At least two species appear in my shell identification book, and sharing many similarities.
Chione mazycki, Dall 1-1½", commonly found in the Carolinas, Georgia and N.E. Florida.
Cross-barred Venus, Chione cancellata, 1-1.75", found from North Carolina to Florida and the West Indies.
Your venus clams are cross-barred venus (Chione cancellata). Nice specimens, nice stripes!
Terri K. Hathaway
Marine Education Specialist
North Carolina Sea Grant