23 
the aperture. Suture shallow. Whorls 5, slightly convex, margined 
at the suture, the last one rounded in the periphery, flattened 
above and below. Aperture broadly ovate, fulvous within; peristome 
thick, continuous, double on account of a small swelling of the lip 
inside its edge, its colour white, except the reddish-orange columel- 
lar lip, which is sunk and sharply set off from the body whorl. 
Columella short, sinuous. Operculum ovate with a thicker disc 
on the inside, the margin of which forms a crest along the co- 
lumellar edge of the operculum. Dimensions: H. 1.5, br. 0.7 mm. 
— Locality: North Island: 3, a few specimens. 
This species belongs to the same group as R. inddata and R. 
lampra as well as the new R. erosa, but it is more siender; it 
recalls the first-named in the occasional appearance of a pair of 
spiral keels. 
Risso a er osa n. sp. 
(PI. I, figs. 12, 13.) 
Shell minute, conical, solid, imperforate. Whorls 5, flattened, 
suture canaliculate.' Spire about 1 1/2 times the aperture in height. 
Protoconch of 1 1/2 whorls, reddish-brown and sculptured with 
minute grains in many very close spiral lines; subsequent whorls 
light yellowish-brown with longitudinal costae separated by narrower 
furrows; above the suture a strong revolving thread; on the last 
whorl the upper half carrying about 22 longitudinal costæ; the 
periphery encircied by a pair of strong spiral cords; base flattened 
and bearing an additional cord. Except for the strong costae and 
ribs only fine lines of growth. Aperture oblique, rounded-ovate; 
peristome thick, continuous, and double, with an interior swelling 
rising from above and below and extending beyond the primary lip 
externally. Columella oblique, sinuous; columellar lip sunk, brown- 
ish. Dimensions: H. 1.5, br. 0.8 mm. — Locality: North Island: 
1, some few specimens. 
Operculum (fig. 13) ovate, with a thin outer layer and a thick 
inner one forming a crest-like edge on the columellar side. 
Rissoina achatina n. sp. 
(PI. I, figs. 5—9; text-fig. 3.) 
Shell elongate conic, imperforate, solid, shining, with faint and 
obsolete axial sculplure, and fine, sharp, undulating spiral striae 
