Isidora lirata, T. Woods, subsp. conferta, n. subsp.

Shell globosely ovate, sinistral, corneous-translucent, thin, almost imperforate, the columellar reflexion leaving only a narrow chink. The distant lines of growth are rather regular, especially on the upper whorls, and under the lens fine regular and close spiral liræ are visible. The colour varies from very light horny to light olive-brown. The spire is short, about one-third the length of the shell. The pullus is acuminate, of darker colour, consisting of two whorls with fine incremental striation. There are four whorls, either strongly shouldered or having only a posterior angle, which usually gets lost on the body-whorl; the latter is forming the greater part of the shell. The base is convex, the suture impressed. Aperture vertical, elongately oval, acuminate above and produced anteriorly. The outer lip is regularly rounded, sharp, thin; the inner lip is twisted, forming a distinct fold near the axis of the shell; not much reflexed. Fig. 7 represents a distinctly shouldered form, and fig. 8 with only a slight angulation on the whorls.

Fig. 7

This subspecies is distinguished from the species by its ventricose form and the much broader aperture, approaching T. tabulata, Gould. I have specimens from two localities:—

(1.) From swamps near Otorohanga, King-country. These are strongly keeled (fig. 7). Three specimens were measured—Shell: length, 11 mm.; breadth, 7 mm. Aperture: length, 7 mm.; breadth, 4 mm. Shell: length, 9½ mm.; breadth, 6½ mm. Aperture: length, 6½ mm.; breadth, 3½ mm. Shell: length, 9½ mm.; breadth, 6 mm. Aperture: length, 6 mm.; breadth, 3¼ mm. The mean rationis are—i. = 1: 1.6; ii. = 1: 1.7; iii. = 1: 1.6.

Fig. 8.

(2.) From Wairau River, south of Birch Hill Station, Nelson. These specimens are much lighter in colour, the upper whorls slightly angled (fig. 8). Three specimens were measured—Shell: length, 11–12 mm.; breadth, 7–7½ mm. Aperture: length, 8–8½ mm.; breadth, 4½ mm. The mean proportions are—i. = 1: 1.6; ii. = 1: 1.9; iii. = 1: 1.4. The means for the two localities are—i. = 1: 1.6; ii. = 1: 1.8; iii. = 1: 1.5.

Type in my collection.

To repeat, the following species are omitted:—

(1.) Physa variabilis, Gray, insufficiently described and unfigured.

(2.) Physa gibbosa, Gould, inhabits Australia.