II. Life History i. Struthiolaria papulosa

the mantle edge as a short, wide rectum. The kidney (Pl. 55, Fig. 3 kd), which as in all marine prosobranchiates gives rise directly to the adult renal organ, is a large flattened or spherical sac on the right pallial wall, extending forward almost to the mantle margin. Its large hexagonal lining cells each contain a dark granular spherule somewhat resembling a nucleus, and the sac undergoes regular pulsatile movements. The two-chambered definitive heart (ht) lies in the pericardium and there is as well a pulsatile larval heart or thoracic vesicle (lh) formed by a dilation of the anterior aorta beneath the pallial cavity floor, which projects in diastole from the aperture of the pallial cavity.

The later development of Struthiolaria papulosa has not been worked out. From the evidence of the 2 ½-whorled protoconch, and the extremely well-developed swimming organs, it seems clear that there is a fairly long stage of planktonic existence. Tow net samples taken at Cheltenham (2.49) yielded one veliger that from size, shell sculpture, and general appearance could be tentatively recognised as a Strutiolaria at the 2-whorled stage, towards the end of larval life. The velum was damaged and withdrawn, although, from the striking resemblance of the four-lobed larva to that of the related Aporrhais, it may well be that, as in the latter genus, the final stage larva of Struthiolaria possesses a six-lobed velum.

ii. Pelicaria vermis

In the genus Pelicaria the embryos are completely incubated in the pouch, and are liberated as tiny replicas of the adult which at once take on a benthic existence. The female reproductive apparatus is in general closely similar to that of Struthiolaria. The albumen gland is, however, shorter, and relatively stouter, the receptaculum forms a smaller bulbous sac, while the capsule gland is relatively more spacious, a single elongate egg capsule occupying its whole length. Only seven or eight capsules are contained in the pouch at one time, each 7 mm. long, elongate-ovoid, not joined in a string, and each containing five eggs, approximately 1·0 mm. across and white in colour (Text Fig. 3). Liberation of the embryos normally takes place when the shell is 4 ½–5 mm. in length, with two rounded whorls and the typical apex of this genus. A thin-walled, elongate, capuliform bulb (Pl. 55, Fig. 4) is placed transversely to the long axis of the shell, being at first transparent and entirely chitinous. It is followed by a calcified spirally coiled region sculptured with fine spiral cinguli from the beginning of the second whorl. As may be seen, this apex differs markedly from the small planorboid tip in Struthiolaria. On liberation, the embryo (Fig. 6), which is translucent milk-white in colour, at once begins in crawl about and to execute the characteristic movements of the adult. The sole is long and narrow, with an opercular spine present by which the typical “righting” movement of the adult can already be performed.

Plate 55, Fig. 5, represents an embryo removed from the pouch at an earlier stage of development. The shell measures 1 ½–2 mm. in length, consisting of a capuliform apex and a single finely spirally sculptured whorl. These embryos move about actively within the capsule, by the action of the foot, and finally break through the enclosing membrane by the use of the opercular spine. A large vestige