Genus Ostrea Linné.
Type: O. edulis Linné.

Ostrea cannoni n. sp. (Figs. 32, 41.)

Shell large, solid, suboval, generally equilateral, rather flat, surface of attachment very large (60 mm. diameter in type). Sculpture of left valve consisting of irregular, discontinuous, waved radial folds which are intersected by a few strong, spaced, puckered, concentric lamellae, numerous crowded fine lamellae towards margins. Ligamental area very large, traversed by fairly deep, concave, triangular pit, about one-third of the total area. Muscular scar oval, nearer the ligamental margin. Valve-margins smooth.

Height 132 mm.; length 128 mm.; thickness (left valve) 50 mm. Maximum thickness of shell material 28 mm.

Locality: Tioriori.

Ostrea waitangiensis n. sp. (Fig. 26.)

Shell fairly large, not heavy, kidney-shaped, with an anterior wing. Surface of attachment moderate. Left valve moderately convex, right valve concave. Sculpture, left valve with short, discontinuous irregular radials, 2–4 mm. wide, developed mostly on the posterior side; and irregular, spaced, concentric lamellae averaging perhaps 15 mm. apart. Right valve with an irregular, puckered surface. Ligamental area destroyed in the single specimen; valve-margins broadly folded.

Height 108 mm.; length 100 mm.; thickness (both valves) 38 mm.

Locality: Cliffs south of Wireless Station, Waitangi.

Ostrea arcula n. sp. (Figs. 42, 43.)

Shell of moderate size, subquadrate, winged posteriorly, beaks inconspicuous. Left valve with a very large area of attachment where it is considerably thickened, but tapers rapidly to a knife-like margin; right valve thin, slightly convex at first but with a deep concavity towards outer border. Surface almost smooth, slightly lamellate towards margins, vaguely puckered posterio-ventrally. Ligament triangular, moderate, directed obliquely backward, with a narrow median groove

Height 40 mm.; length 40 mm.

Locality: Momoe-a-toa