Mauidrillia incerta
Shell of moderate size, with a tall, narrow spire, and a relatively short siphonal canal. Shoulder moderately wide, steep, lightly concave. Sinus typical of the genus. Twelve axial folds on both the penultimate and the last whorls are bluntly rounded at the periphery, fade out rapidly over the shoulder, and reach to the lower suture on spire whorls and to the beginning of the unusually well-marked basal constriction on the last whorl; axials moderately high, rounded, spaced their own width apart, slightly oblique. Spiral sculpture consisting of a relatively very prominent subsutural cord, six low, weak cords on the shoulder, increasing in strength towards the periphery, nine more prominent ones at and below the periphery on sides of penultimate whorl, and about 30 on sides, base, and canal of last whorl, of which
about 10 occupy the sides; the two peripheral cords are slightly more prominent than any others, and have a single interstitial thread. Protoconch missing. Outer lip broken away for the whole of its length, so that the shape of the tip of the canal is not known. Dimensions: height, 12.9 mm; diameter, 4.3 mm (holotype).
Locality: N165/947, GSI0201 (= V 1951), McLeod’s Stream, Mangaopari, unique holotype. Holotype (TM4650) in New Zealand Geological Survey.
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This species is similar to the Waitakian and Otaian M. inaequalis Powell, 1942, and the Hutchinsonian or Otaian M. imparilirata Powell, 1942, in general appearance, in having nodules reaching the lower suture but not the upper one, and in having weak spirals over the whole shoulder; however, it differs from both in having a taller spire and a more prominent subsutural cord, from M. imparilirata in having rounded nodules at the periphery and a much more elongate form, and from M. inaequalis in having a markedly more contracted base and a shorter siphonal canal. The lack of the protoconch and of the tip of the canal leave some doubt of the generic position, but the inner lip lacks the callus pad of Splendrillia. The new species is placed in Mauidrillia because of its close resemblance to the other species mentioned.
Mauidrillia had not been reported above the Awamoan before, apart from the Opoitian (early Pliocene) M. acuta (Marwick) ; the new Tongaporutuan species helps fill a large gap in its time range in New Zealand