Amphipeplea arguta, Hutton (1885).
Trans. N.Z. Inst., vol. xvii., p. 54, pl. xii., fig. 1.
(1.) Lake Waikare (Stat. 19 and 19F—From reeds).—Fourteen
mostly young shells. Colour horny, columellar lip broadly reflexed. Dimensions—Shell: length, 7 mm.; breadth, 4 mm. Aperture: height, 5 mm.; breadth, 4 mm. Shell: length, 5½ mm.; breadth, 4 mm. Aperture: height, 4½ mm.; breadth, 3 mm.
(2.) Lake Taupo (Stat. 42—With weeds from 20 ft. to 80 ft.).—One specimen collected alive; yellowish-white, rather slender. The aperture more elongated than in the type. Shell: length, 5½ mm.; breadth, 3½ mm. Aperture: height, 4 mm.; breadth, 2½ mm.
(3.) Lake Wakatipu (Stat. 10—Dredged with weeds in 200 ft. to 300 ft.).—One specimen collected alive; nearly colourless, transparent, very thin and fragile, with broad columellar reflection; regular distinct incremental lines. The aperture is longer and narrower than in the type. Shell: length, 5¼ mm.; breadth, 3¼ mm. Aperture: height, 4½ mm.; breadth, 2½ mm.
(4.) Lake Wakatipu (Stat. 33—Dredged in 30 ft. to 60 ft.).—Two specimens collected alive. A slender form with elongated aperture, of horn-colour, with regular lines of growth, and the spire a little higher than typical. Shell: length, 5 mm.; breadth, 3 mm. Aperture: height, 3½ mm.; breadth, 2¼ mm. Shell: length, 4 mm.; breadth, 2½ mm. Aperture: height, 3½ mm.; breadth, 1¾ mm.
The Dentition.—Figs. 11–14 represent the most characteristic teeth of the radula of specimens from the four localities—fig. 11 from Lake Waikare, fig. 12 from Lake Taupo, fig. 13 from Stat. 10, and fig. 14 from Stat. 33, Lake Wakatipu. Compared with Hutton's description and figure of his species* a considerable variability, especially in the transitional teeth, is at once apparent. The central tooth shows mostly a second small denticle on the left side; the lateral teeth have all three cutting-points, but the entocone and mesocone may coalesce, forming only one cutting-point, as was evidently the case in the example
[Footnote] * Trans. N.Z. Inst., xvii., p. 54, pl. xii., fig. 10.
figured by Hutton. The number of laterals and marginals is very variable, and the figures sufficiently show the different arrangements of the cutting-points on the transitional teeth.