Shell size to 150 mm; shell thick, more inflated than in Mercenaria mercenaria, ovate-trigonal. Sculpture of irregular lines, more separated than in M. mercenaria. Lines never absent in middle of valve. Lunule as long as wide. Color dull-white to gray. Internally sometimes stained with purple. This species hybridizes with M. mercenaria in the southeastern United States. Juvenile shells (additional photo, size 30 mm) have purple zigzag lines; do not confuse these with Chione elevata or Chionopsis intapurpurea.