As in most incubating molluses, reproduction probably takes place all the year round, ovigerous females being collected at Auckland during November, December, April, June, August, and September. As many as 1,000 to 1,500 capsules are contained in the pouch, and a total of 20,000–30,000 veligers are thus liberated from a single brood. An early stage in development removed from the pouch (Pl. 55, Fig. 2) represents an abbreviated two-lobed veliger, approximately 0·5 mm. in length, with a pair of short, undivided velar rudiments projecting laterally. The visceral mass is opaque and yolky, covered by a shell rudiment, in the form of a delicate chitinous cap, while the head region forms a large spherical protuberance with neither eyes nor otocysts visible. The foot is present as a short, tongue-shaped lobe, behind the head, and the embryos move about freely within the capsule, mainly by muscular movements of the velar lobes.

At the final stage in incubation, when the capsules have attained approximately twice their original size, and the large four-lobed veligers can be clearly identified within, the pallial margin is widely extended over the lip of the shell, bringing the pouch aperture to an external position, and a string of capsules is extruded, the veligers at once breaking through the capsule membrane and commencing to swim freely. The expanded velum (Pl. 55. Fig. 1 VL.) now measures 1 ½ 2 mm. across, deeply subdivided to form a pair of large swimming lobes at either side. Near the tip of each lobe is a very conspicuous yellowish-brown spot, from which a yellow band extends around the velum just inside the margin. The thickened rim of the velum is beset, with stiff, robust, cilia, approximately 15μ in length, which serve, together with movements of the velar lobes themselves, for the rapid propulsion of the larva. The larval shell (sh) is at this stage 0·3 mm. in height and a little less in width, chitinous, perfectly transparent, without sculpture and forming a tiny wide-mouthed cup. with a short, single-whorled planorboid coil. The foot (ft) lying behind the velum is narrow and squarish along the anterior edge, becoming wider and oval behind, the whole surface glandular and finely ciliated. No opercular rudiment is yet present. The cephalic tentacles are short and clubshaped, tipped with several longish sensory cilia. The eyes are prominent at the tentacle bases, and the otocysts distinctly seen within the head cavity. The etnidial filaments are not yet elongated as in the adult, and ciliary feeding apparently does not occur at this stage.

The alimentary canal (Pl. 55, Fig. 3) shows essentially its adult form. The buccal bulb with its minute radular rudiment leads into the narrow, strongly ciliated oesophagus, passing back to the stomach—a transparent globular sac, provided with a short caecum from which projects a perfectly developed crystalline style, rotating clockwise 40 times a minute, with a mucus-bound mass of food material attached to the gastric end. The two digestive gland lobes are filled with brownish yolky contents, and there is a two-way pasage of particles along the diverticula leading out of the stomach. The intestine is a narrow ciliated tube encircling the renal organ, and continuing to