Shell with a strong nodulous angle at the middle of the whorls, with a row of smaller nodules just below suture; the two rows of nodules sometimes united, forming short ribs; surface everywhere covered with strong, revolving, thread-like sculpture; upper canal small; basal canal short, reflexed. Color blackish, with broken, revolving white lines; aperture blue, becoming blackish farther in.
Length, 25; diameter, 10 mm.

Cerithium atratum (Born, 1778) Dark Cerith
Distribution: North Carolina, Florida, Texas; Brazil. Size: 25 to 38 mm.
Description: Color of base whitish, with spiral brownish bands; shell shape elongate, turriculate; sculpture consists of numerous weak, flat-sided convex whorls, possessing numerous rows of spiral beaded cords on each whorl, with fine granulated threads between the beaded cords, remnants of what were once varices on each whorl; spire pointed; aperture oblique with outer lip crenulated into a thick varix; siphonal canal and anal canal well developed; operculum paucispiral, brown, and corneous. Habitat: Found on limestone, sand, and rubble and on Thalassia in shallow water. Remarks: Differs from C litteratum by its narrower form and smaller beads. Also commonly called the Florida cerith. See Houbrick (1974a, 1974b); Andrews (1977). Synonym: C floridanum Morch, 1876.