Cerithium placidum Gould, 1861. Length, 5 mm; diameter, 1.5 mm. Shell: elongate-conic, slender; with obsoletely beaded spiral threads; usually white. Spire: protoconch of four brown whorls, the two apical whorls smooth, the remaining two with spiral keels; teleoconch of about 10 slightly convex whorls; suture shallow. Sculpture: two or three apical whorls below the protoconch with a barely beaded spiral and a smooth spiral thread, abapical whorls with about seven delicately beaded spiral threads, the interspaces twice the diameter of the threads and faintly striated. Aperture: sub-ovate, outer lip thin; base concave, encircled apically by a beaded spiral; anterior canal short, barely recurved. Color: variable — usually white but sometimes light brown or lavender.
Shells are common in beach drift and occasionally found in sediments to depths of 26 m.
C. placidum was described from Okinawa. Shells are distinguished from those of C. interstriatum by their smaller size, usually finer sculpture, and by the predominantly spiral sculpture of the apical whorls (the apical whorls in C. interstriatum are clathrate).