2. Serpulorbis aotearoicus sp. nov.

This species resembles zelandicus in adult shell characters, tending to a darker brown or purplish-brown colour, but without apparent difference in sculpture. The coloration of the animal is, however, quite distinctive. The predominating colour of the head, proboscis and foot is black, or at times a lighter shade of greyish, lightening to pinkish-brown further back on the trunk and proximal parts of the foot. The tip of the proboscis is always deep black, and along the margin of the cephalic shield is a bright yellow or yellowish-cream line, passing backwards from the base of the short cephalic tentacle, which is itself yellow. A margin of the terminal pedal disc forms a broad band of yellow, and the black pedal disc itself is closely flecked or striated with yellowish. The pedal tentacles are mottled with black and yellow. The mantle is light brown in colour, its border edged widely with bright orange-red. The viscera are pure white, the digestive gland black. The opereulum is absent in the adult.

The radula (Text-Fig. 2) is distinguished from that of zelandicus by the narrowness of the central and lateral teeth, which are slightly greater in length than in breadth. The principal cusp of the central tooth is much smaller than in zelandicus, usually not more than a quarter the length of the tooth. The basal wings of the central tooth are shortly truncated, and the lateral teeth set closer to the mid-line. Their mesial cusps are also much smaller than in zelandicus.

The embryo shell of aotearoicus is illustrated in Figures 20–24. The nucleus is of one and a half whorls, with the apex a transparent spherical bulb, soon developing a finely lirate longitudinal sculpture, crossed by very delicate accremental striae. The lirate portion of the nucleus gives place abruptly to a second whorl which is without longitudinal sculpture, though marked with fine, distinct growth striae, and tinted with several longitudinal splashes of reddish-brown. The aperture at the one and a half whorled stage is approximately triangular, slightly notched or effused at the inner lip. The shell is at this stage imperforate, but the coiling early begins to loosen up, and the earliest part of the attached shell has the appearance of Fig. 25, somewhat resembling a worm tube of Spirorbis. The embryo at the free-moving two-whorled stage has a large chitinous operculum, concave or saucer-shaped, with the margin simple.

Type in the Auckland Museum. Slide of radula and colour record of living animal are deposited with the type. Paratypes in the Zoology Museum, Auckland University College.

Localities. Milford Reef, Rangitoto Channel (type)—under boulders at low spring tide, on outer fringe of reef, together with smaller numbers of zelandicus; Otata Island, Noises Group, on exposed rocks, covered with Melobesia at low spring tide.

Complete correlation was found in radula and animal coloration for 50 specimens of aotearoicus and 16 specimens of zelandicus examined from Milford. The two species occur intermixed in the same locality,