Sinezona hawaiiensis n. sp.

Figure 4

Type material. Holotype (LACM 2466), leg. Twila Bratcher. Type locality. 30 m, off Waikiki, Oahu, HI, USA, 21.270˚N, 157.840˚W.

Etymology. Named after its provenance from Hawaii, USA.

Description. Shell small (0.5 mm), trochiform, globular. Protoconch of 1 whorl, with fine axial cords, no apertural varix. apertural margin prosocline. TI of 1.25 whorls. Shoulder with broad indistinct axial cords, approximately 30 on first whorl, without discernible spiral sculpture. Base with axials becoming more distinct towards umbilicus, approximately 13 low spiral cords between periphery and umbilicus, barely noticeable at periphery, becoming as strong as axials towards umbilicus. TII of 0.125 whorls, same sculpture as on TI. Umbilicus very narrow, bordered by strong cord, walls with distinct growth marks, no funiculus. Selenizone absent, foramen oval, keels low, strong. Aperture rounded, roof overhanging. Animal unknown.

Differential diagnosis. Sinezona haliotimorpha (Bandel, 1998) from the Oligocene of France has a protoconch with fewer and stronger axials, and a teleococh with stronger axials and consistently finer spiral threads on the base, as well as a foramen with more elevated keels. Sinezona brevis Hedley, 1904 [= Ariella campbelli Bandel, 1998] from New Zealand has a protoconch like S. haliotimorpha, has a greater expansion rate of the shell giving it a more oval appearance, and when fully grown has a short selenizone.

Distribution. Known only from type locality.

Remarks. The absence of a selenizone has been taken as genus-level character by Bandel (1998) to establish Ariella Bandel, 1998. Marshall (2002), however, pointed out that there is significant intraspecific variability in the length of selenizone, with some species [e.g., Sinezona brevis (Hedley, 1904)] showing a distinct to no selenizone at all. Accordingly, the absence of a selenizone is not considered significant for generic classification. Equally, the presence and absence of a protoconch varix and details of teleoconch ornamentation vary extensively between species in the same genus and is also insignificant for beta taxonomy (Geiger 2003).

The shell appears mature due to the descending apertural margin on the last portion of the whorl. The species is known from a single, but well-preserved specimen. The difference in protoconch sculpture, and the absence of any sign of a selenizone despite the sloping aperture indicating maturity, refutes the possibility of a mislocalized specimen from New Zealand.