Niso basiglobosa n.sp. (Plate 24; Figs. 19, 20.)
Shell of moderate size, narrowly conic. Protoconch eroded in the single specimen. Whorls 12, height of each about three-eighths diameter, sides flat. Surface somewhat pitted by weathering, growth lines weak, a number of oblique, slightly concave growth pauses well defined. Suture inconspicuous. Body-whorl slightly over one-third total shell height, regularly rounded on the periphery. Umbilicus moderately large, its walls curved and merging gradually into the base without any ridge. Aperture relatively short, with just a suggestion of an anterior beak. Outer and inner lips thin, parietal wall without callus.
Height: 17 mm.; diameter. 6.5 mm.
Locality: Opua River, a quarter mile below Gorge Bridge, Kakahu (Bortonian), P. B. Maling coll.
The absence of a ridge bounding the umbilicus and the rounded periphery show that this shell is off the main line of Niso descent. Cossman and Peyrot's N. degrangei from the Helvetian of Aquitaine is similar though it has a sub-angulate periphery, straighter umbilical walls and, therefore, a better defined beak. N. angusta Desh. from the Paris Basin Eocene has a rounded periphery but a smaller umbilicus. Cossman and Peyrot (1917, p. 286) stated moreover that the protoconch of degrangei has a heterostrophic nucleus. This confirms the evidence of the other characters that this species does not belong to Niso restricted, and perhaps not to Niso even in a wide sense. It should at least be subgenerically separated. Whether angusta or the new species belongs to this group or to another one cannot be decided until the protoconchs are known.