Cavellia biconcava (Reeve 1852)

Distribution

Lower North Island (including Kapiti Island).

New Zealand Threat Classification System

Not Threatened

Bio Status

Indigenous (Endemic)

Description

Shell small, about 4.8mm at 5 whorls, biconcave, axially ribbed, broadly umbilicate, glossy. Colour translucent pale buff with broad, brown, irregular axial bands. Spire concave; umbilicus about 50% of max. shell diameter. Protoconch of 1.3 whorls, ornamented with thick axial ribs and traces of interstitial axials but spiral lirae missing. First quarter of embryonic shell smooth, then axials appear, these becoming gradually more closely and regularly spaced and more rounded. Teleoconch whorls loosely coiled, convex, increasing regularly. Sculpture consisting of strong primary axial ribs without periostracal lamellae and much thinner interstitial secondary axials, these crested by short periostracal lamella. Axials distinctly protractive above, arcuate on periphery, thence flexuous and gently directed backwards. Spiral lirae are absent, giving the shell a shiny gloss. Aperture round, outer lip retracted at suture leaving a distinct sinus. Columella short, slightly expanded; parietal wall with a broad shining whitish glaze.

Habitat

Litter dweller in forests and shrublands up to 1220m; also found in scree and under logs and rocks.