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Cystiscus cratericula (Tate & May, 1900)

Diagnosis: Shell small, colourless transparent to opaque white; spire immersed; outer lip thickened internally, smooth; external varix absent; siphonal notch absent; posterior notch absent; lacking collabral parietal callus ridge; columella with only two plaits, the first very strong, and no lirae.

Size: Up to 3.5 mm in length, commonly about 2 mm.

Distribution: Australian Museum collection: Sydney, NSW, to Great Australian Bight , WA , and Tasmania , in 53-549 metres.  Uncommon.

Comparison: This species appears to consistently have only two plaits on the columella, the first very strong; this character separates it from the rest of the family.  The species varies in length to width ratio, with most specimens being more elongate than the type illustrations.  Elongate specimens are similar to C. connectans, but may be separated by the columellar plaits.

Synonymy: Marginella inaequidens May, 1913 (Hewish in Wilson, 1994)

Fig. 1: The specimen figured by Laseron (1948, fig. 20); off Twofold Bay, NSW, in 110 m (C.336615)

Fig. 2: Paratype of M. inaequidens May, 1913. Off Cape Pillar, Tasmania, in 183 m (C.034116).

Copyright Des Beechey 2004