Placid Periwinkle

Shell size to 15 mm; shell pointed, solid, whorls with flat sides. Sculpture consisting of widely spaced spiral grooves. Aperture length about half of shell length. Color white with dark-brown, wavy or zigzag lines, and broad band of purplish-brown color on median part of last whorl; this band also visible in abapical part of previous whorls. Found on splash zone (supralittoral), on rocks or other hard substrates. Species previously listed as Nodilttorina interrupta (Philippi, 1847). The supplementary photo was taken by Diane Dringoli Thomas in October 2019 on the bay side of Sanibel.