Genus Isidora, Ehrenberg (1831).

Isidora tabulata, Gould, subsp. moesta, H. Adams (1861). P.Z.S., 1861, p. 144.

(1.) Lake Waikare (Stat. 19—From reeds).—One specimen only was obtained. It is of light-horn colour, very thin, covered with a greenish coating; there are four whorls, the last two distinctly shouldered and keeled. Columella excavated in the middle, fold distinct, reflection of columellar lip small; outer lip sharp, regularly arched. It is a little more slender than the type. Shell: length, 7 mm.; breadth, 4 mm. Aperture: height, 5 mm.; breadth, 2½ mm. Ratios: i. = 1: 1.75; ii. = 1: 2; iii. = 1: 1.4. (The ratios are the same as in the revision of Isidora.)

(2.) Lake Waikare (Stat. 28—From weeds in water from 1½ ft. to 2 ft.).—Two specimens of dark-brown colour, solid and large, keeled, the keel becoming obsolete on approaching the aperture; columella twisted. They differ but little from the type. Shell: length, 17½ mm.; breadth, 11 mm. Aperture: height, 11 mm.; breadth, 6 mm. Shell: length, 14 mm.; breadth, 9½ mm. Aperture: height, 10 mm.; breadth, 5 mm. Ratios: i. = 1: 1.6; ii. = 1: 1.8; iii. = 1: 1.6. i. = 1: 1.5; ii. = 1: 2; iii. = 1: 1.4. The accompanying fig. 15 shows some teeth of the radula, which need no explanation. The dentition of our forms of Isidora is so variable that I doubt whether it can be used as a help to separate the species. However, a considerable number of animals of each species has to be examined before this point can be settled definitively.

Fig. 15

(3.) Lake Waikare (Stat. 28F—From weeds in water from 1½ ft. to 2 ft.).—Two “dead shells,” one young, the other nearly adult. They resemble those from the last station, but are a little more ventricose, and have the spire a little shorter. Shell: