Sphærium novæ-zelandiœ, Deshayes (1853).
Cat. Conchif. Brit. Museum, p. 272; P.Z.S., 1854, p. 342.
(1.) Lake Rotoiti (Stat. 15—From muddy bottom and weeds in 6 ft.).—Three specimens of nearly equal size, suborbicular, subequilateral; colour grey, near the ventral margin yellowish; beaks covered with a ferrugineous incrustation. Nepionic shell
hardly to be distinguished from the later growth, obtuse; anterior side of shell slightly produced, rounded, posterior side broadly convex; the whole of the valves concentrically finely striate. Ligament inset. Left valve with a straight lamellar upper cardinal, and below and slightly in front of it a curved stouter tooth. In the right valve the two cardinals are united, forming an oblong squarish tooth with three denticulations on the lower margin. Laterals smooth. Fig. 5 illustrates the cardinal teeth of the two valves. Length, 5 mm.; height, 4¼ mm.; diam., 2¾ mm. Umbo 3 mm. from anterior end. The indices are—iii. = 85; vii. = 55; x. = 60.
This is no doubt the same as S. lenticula, Dunker, as Hochstetter obtained the specimens from the lakes Rotoiti and Taupo, and I consider it as a synonym of S. novæ-ze-landiæ.
(2.) Lake Taupo (Stat. 4—Dredged with weeds in 20 ft., and from bottom of coarse pumice in 100 ft.).—Four specimens of straw colour, the nepionic shell rather distinct, but otherwise not differing from the typical form. Right valve with two minute cardinals, the anterior oblong, the posterior short, triangularly oval, elevated. Left valve with two minute teeth, broadly rounded behind, pointed at the anterior end, one in front of the other. Fig. 6 shows the form and position of the cardinals. Length, 4½ mm.; height, 4 mm.; diam., 2½ mm. Umbo 2¾ mm. from anterior end. Indices—iii. = 84–89; vii. = 56; x. = 61.
(3.) Lake Taupo (Stat. 34—With weeds from 20 ft. to 80 ft.).—Six small specimens, a little more oval and compressed, but otherwise the same as the examples from Stat. 4. Length, 4 mm.; height, 3 mm.; diam., 1¾ mm. These are the dimensions of Dunker's S. lenticula. Indices—iii. = 75; vii.—44.
(4.) Lake Waikaremoana (Stat. 33—Dredged in 10 ft. to 20 ft.).—There are twenty-three small to minute specimens. The larger examples are yellowish-grey, the small ones straw-colour. In the right valve there are two lamellar cardinal teeth meeting at an obtuse angle; in the left valve there is one crescent-shaped
rounded cardinal, and a strong bifid crenulated cardinal below and slightly in front of it. Fig. 7 illustrates the cardinals of the valves. The lateral teeth are smooth; the ligament inset. Dimensions of two specimens—Length, 4¼ mm.; height, 3½ mm.; diam., 2 mm.; beak 2½ mm. from anterior margin: length, 4 mm.; height, 3½ mm.; diam., 2 mm.; beak 2¼ mm. from anterior margin. The mean of the indices is—iii. = 85; vii. = 49; x. = 58.