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ORBITESTELLIDAE

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Obitestella bastowi (Gatliff, 1906)

Description: Shell minute, spire sunken. Protoconch of about 1¼ whorls with raised spiral ridge on dorsal surface. Dorsal surface of teleoconch whorls with a strongly nodulose, broad spiral cord on inside of spiral, surrounded on the outside by shallow groove before weakly nodulose upper peripheral cord. Lower peripheral cord weak or absent. Base with widely open umbilicus, surrounded by broad spiral cord as on the dorsal surface. Shell transparent, becoming opaque white with age.

Size: Up to 0.9 mm in width.

Distribution: Ulladulla, NSW, southwards to Eyre Peninsula, SA, including Tas.

Habitat: Specimens are from rock and algal washings from the intertidal and from dredgings down to 100 m. Uncommon.

Comparison: The three NSW species of Orbitestella can be separated by sculpture:

• O. decorata has a strongly nodulose spiral cord on the dorsal surface, and strongly nodulose cords on the periphery.

• O. bastowi is strongly sculptured on the dorsal surface, but the upper and lower peripheral cords are weak, or sometimes absent.

• O. wareni has the upper and lower peripheral cords weak, or sometimes absent. The whole surface has axial folds that originate on the dorsal surface, cross the periphery and continue on the base.

Figs. 1–3: Bittangabee, N of Green Cape, NSW (C.355511).