Cerithiopsis arga Kay, new species. Length, 5.5 mm; diameter, 1.25 mm. Shell: slender, subcylindrical; with three rows of beaded spiral cords on each whorl; glistening cream with a brown line at the suture, occasionally ail brown or ail white. Spire: protoconch of four and one-half slender, conical, smooth whorls; teleoconch of eight to twelve rather flat-sided whorls; suture shallow, channeled. Sculpture: spiral sculpture of three subequal, close-set, beaded cords with narrower interspaces and a smooth cord at the margin of the base of the last whorl; axial sculpture of ribs recessed below the spirals; suture with a fine spiral thread. Aperture: subquadrate; outer lip thin; columella straight; siphonal canal barely produced. Color: variable — glistening cream with a brown spiral at the suture and with the base of the last whorl brown, sometimes ail cream or ail brown.
This is the most common of the Hawaiian cerithiopsids, found in beach drift, in sediment on reef flats, and to depths of 60 m. The shells are variable in both size and color. The holotype, 5.5 mm in length, with 10 whorls, cream colored with brown suture and base represents the most often encountered color form. The veliger larvae are bilobed, the apical lobe twice the size of the abapical lobe; they metamorphose when four to four and three-quarters whorls are complète, at a length of 600 to 700 µm (J. B. Taylor, 1975).
Type locality: Kepuhi Point, Oahu, from a depth of 6.5 m. Holotype: Bernice P. Bishop Muséum No. 9745. Paratypes: Australian Museum, British Museum (Natural History), United States National Museum.
The Hawaiian shells are distinguished from those of C. rubricincta Melvill, 1896, from Bombay by their broader outline and three rows of granules (there are two in C. rubricincta), from those of C. filofusca (Laseron, 1951) from New South Wales and C. orientalis Preston, 1905, from Ceylon by the narrower protoconch base; and from those of C. hedista Melvill and Standen, 1896, from Lifu, in color pattern (the abapical spiral in shells of C. hedista is honey yellow). Derivation of name: Greek adjective meaning shining or glistening. Refers to the glossy surface.