Genus Ascitellina nov.
Type: Ascitellina donaciformis Marwick.
Shell small, anterior end produced, narrowly rounded; posterior end short and broad. Sculpture of fairly strong concentric ridges. Hinge with two divergent cardinals the posterior one bifid; no laterals. Ligament external, nymphs exposed but narrow, sunk below margin, and descending posteriorly. Pallial line unknown.
Ascitellina donaciformis n. sp. (Figs. 59, 60.)
Shell very small, longitudinally oval; beaks behind the middle line, inconspicuous; anterior end long and narrowly rounded, posterior shorter and broader, roundly truncated. Sculpture of fine,
sharp concentric ridges, about 8 per millimeter on the centre of disc, many die out on reaching the posterior area where the remainder become thicker, about 4 or 5 per millimeter. Hinge weak: right valve with a narrowly-triangular, grooved posterior cardinal tooth, and a weak lamellar anterior one; no lateral teeth; ligamental nymph short, sunk below the valve-margin. Pallial line not seen. Valve-margins smooth.
Height 6 mm.; length 10 mm.; thickness (1 valve) 1.4 mm.
Locality: Cliffs below Wireless Station, Waitangi.
The only closely related New Zealand shell is an undescribed species from the Waiarekan tuffs, Lorne. It is of the same size and shape but the concentric ridges are much further apart.