As Janthina prolongata

25mm. Fragile, translucent, globose, low spired with deep sutures. Aperture very large, elongate anteriorly. Columella smooth, sinuous; lip usually imperfect. No umbilicus. Silky surface has faint axial striae forming chevrons at periphery. Violet, paler below suture on last whorl. Habitat: floats passively, sometimes beached. Distribution: Persian Gulf, Gulf of Oman, Yemen

Shell globose, very thin and fragile, plicately striated, polished. Sculpture consisting of oblique growth-striae and plications, sharply sinuated below the middle of the last whorl, where there appear a few fine spiral lines ; base with a few distant spiral incisions. Colour light violaceous, whitish below the suture, but darker on the base. Spire short, slightly immersed ; outlines convex. Protoconch minute, pupiform. Whorls about 7, first slowly then rapidly increasing, convex, indistinctly biangulate ; base convex. Suture deep. Aperture large, oval, higher than broad, produced into a short open channel at the base, rounded above. Outer lip regularly convex, with an angular not very deep sinus. Columella vertical, very little twisted, terminating in a point below. Inner lip very little expanded beyond the columella, forming a thin callus on the parietal wall.
Diameter, 38 mm. ; height, 41 mm. (large specimen).
Animal unknown.
Hab.—North Island, not common.

Janthina globosa Swainson, 1822. (Synonym: Janthina prolongata Blainville, Laursen, 1953.) Height, 18 mm; diameter, 18 mm. Shell: globose; spire short; aperture large; dark violet. Spire: whorls and apex somewhat depressed; suture distinct. Sculpture: fine striae curving over a low spiral keel on the last whorl. Aperture: relatively large for the size of the shell; columella twisted. Color: dark violet.