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Attenuata imbrex (Hedley, 1908)

Description: Shell moderately elongate, spire weakly convex. Protoconch smooth, terminating with strong varix at junction to teleoconch. Teleoconch up to 4 convex whorls. Whorls sculptured with 2 strong spiral cords on lower half, upper half smooth; last whorl with base smooth, or with obsolete spirals. Aperture nearly circular, anterior canal broad, without posterior channel. Outer lip not thickened in available specimens. Umbilicus a narrow slit. Colour translucent fawn or opaque white.

Size: Holotype 3.6 mm in length.

Distribution: Holotype and paratypes from Middle Harbour, NSW; other Australian Museum specimens from Twofold Bay, NSW. Laseron (1950) listed records from three locations in Sydney Harbour and one from off Crookhaven, NSW, but there is doubt that his identifications are correct (see Remarks below).

Habitat: Type specimens apparently beach collected. Rare.

Comparison: This is like A. praetornatilis and A. archensis, but more elongate.

Synonymy: None.

Remarks: Laseron (1950) said that this species was "readily recognised by its elongate form, strong double keel and striate protoconch". The elongate form and double keel are good characters, but the holotype and paratypes have a smooth protoconch. Hedley's original illustration (Fig. 2) suggests an axially striate protoconch, but the protoconch of the holotype actually has the first half whorl missing, while the second half is smooth. Hedley's figure also suggests that the holotype has axial and spiral microsculpture over the whole surface, but the shell actually has a smooth, slightly abraded surface. 

Fig. 1: HOLOTYPE Middle Harbour, NSW (C.29110). Photo: Australian Museum

Fig. 2: Figure from original description by Hedley (1908)


Copyright Des Beechey 2010. Amended 2014.