blunt, very little compressed and not connected by sharp carina as in true dilatata. Periphery angled. Shoulder slightly concave. Adult lip not dilated. Colour buff; interstices of spiral sculpture obscurely lined with light brown. Aperture, interior of canal and parietal wall porcellaneous white. Margin of outer lip showing small dark-brown blotches caused by interstitial colour lines of exterior showing through callus. Protoconch damaged in both specimens.

Operculum (Fig. 2) horny, terminal nucleus inside with whitish marginal callus typical of dilatata. Differing from that of typical species in flattened upper outer slope, forming an angle of 52° with axis and also in the nuclear pad of the inside which is much less prominent.

Height 136 mm.; diameter 59 mm.; (holotype) (Fig. 13).

Height 150 mm.; diameter 67 mm.; (paratype) (Fig. 14).

Holotype and one paratype in Author's collection, Auckland.

Habitat: off Cuvier Island, Bay of Plenty, in 38–40 fath.

The slightly changed operculum proves morphological divergence indicated by shell characters.

Verconella dilatata var. rotunda n. subsp. (Figs. 11, 12).

Differs from the typical species in having the whorls more rounded, the periphery only slightly angled, the carina composed of several ribs of equal strength produced into squarish nodules, and the spire proportionately shorter. Outer lip of aperture dilated and marked with colour-blotches as in typical species. Colour-markings absent from 40–50 fathom shell. Operculum, protoconch, and number of whorls same as those of typical species.

Height 150 mm.; diameter 72 mm. (holotype) (Fig. 11).

Holotype and one paratype in Author's collection, Auckland.

Habitat: off Whakatane, Bay of Plenty, in 25–30 fathoms. (Type) also from 40–50 fath. off Whakatane.

This specialised form is the Eastern Bay of Plenty equivalent to the 20–25 fath. typical dilatata of the Hauraki Gulf and North.

So far, rotunda has been observed only from off Whakatane. Charts of the Bay of Plenty show a shallow-water connection of about eight fathoms between Matata and Rurima Rocks.

V. dilatata and its allies are never found in less than eighteen fathoms, so this shallow-water arm forms a natural division and barrier to the dispersal of the inshore fauna. Thus through partial isolation, east of the barrier, this new form is diverging from the ancestral type. As its differentiating characters are confined to the shell, the operculum not reflecting any morphological change, this form is indicated as a species in the making which can conveniently be classed as a sub-species.

No intermediate forms have been observed, and the differences in shell characters are readily distinguishable at sight. Occasionally

rotunda ranges down to 40–50 fathoms, a specimen being trawled alive together with the deep-water form of dilatata which, however, is directly related to the inshore typical dilatata from west of the barrier.

Verconella elongata n. sp. (Figs. 23, 24.)

Differs from dilatata in being proportionately much narrower with shoulder descending at a much sharper angle, canal straighter, outer lip not dilated and minus colour-blotches. Operculum distinct.

Shell large, solid, canal long, almost straight, narrowly open. Whorls nine. Protoconch of three and a half whorls, shaped as in dilatata. Height of spire and strength of peripheral nodules variable. Outer lip sinuous at shoulder, not dilated, lirate within, minus marginal colour-blotches, shoulder straight sharply descending, forming an angle of 30°-32° with vertical axis of shell (40°-50° at outer lip), in dilatata the angle is about 45° (55° at outer lip). Sculptured with numerous very fine spiral lirae alternating with stronger spiral riblets. Colour buff with the riblets light reddish-brown. Inside aperture and canal white, parietal wall whitish with light brown of body-whorl showing through. Operculum (Fig. 3) differing from that of dilatata in the flattened upper outer slope which forms an angle of 52° with axis. It is very close to the operculum of dilatata cuvieriana but in that species the nuclear pad of the inside is much less prominent than in dilatata and elongata.

Height 129 mm.; diameter 53 mm.; (holotype) (Fig. 23).

Height 134 mm.; diameter 55 mm.; (paratype) (Fig. 24).

Habitat: Quarter of a mile off Whale Island, Bay of Plenty, in 19 fathoms. (Type) near Whale Island in 19–20 fathoms.

As in the case of the preceding subspecies of dilatata the same factor of isolation from main stock seem to have caused the divergence of still another form, so distinct from dilatata that full specific distinction is warranted. This species has been obtained only from the vicinity of Whale Island, off Whakatane, in 19–20 fathoms. The shallow-water arm stretching from Matata to Rurima Rocks, mentioned above, is no doubt the direct cause of the divergence, the inshore Whakatane colonies being thus isolated from those west of the barrier.

Verconella ormesi n. sp. (Figs. 15, 16, 17.)

Shell very large, thin, canal short, slightly curved and widely open, spire tall. Aperture + canal 0.971 times greater than height of spire (holotype). Whorls eleven. Protoconch (Fig. 9) of four convex whorls, first four or five post-nuclear whorls axially costate and slightly keeled, succeeding whorls rounded, slightly appressed towards suture. Sculpture similar to that of dilatata consisting of numerous very fine spiral striae alternating with stronger spiral riblets. Aperture faintly lirate within. Outer lip thin, not dilated, slightly flexuous. Inner lip spreading as a thin callus across parietal wall and inner edge of columella. Occasional aged specimens with

First line of second paragraph under Group B should read adusta, Shell large, solid, heavy, Whorls sharply angled at periphery To face page 556

Strait must have been closed and a continuous beach must have extended from Kahurangi Point to the Wanganui area. This would effectively account for the occurrence of this and many other species of southern origin now found in the Wellington district.

Mandarina which is typical of the rocky littoral of the South is replaced in similar stations in northern New Zealand by the nodulous-angled adusta. In northern sandy and deep-water localities, a mandarina-like form has developed which, however, can be traced by the unequal inheritance of nodules and peripheral keel in some specimens to northern adusta.

In the light of modern evolutionary conceptions, it now becomes difficult to define a species, many apparently distinct types being bridged by the occasional occurrence of intermediate forms when bathymetric and littoral series from a variety of formations are brought together. As the extremes, however, represent the evolutionary forces at work, it is best to recognize extreme variation from the named type when comparatively stable as of sub-specific rank, being really species in the formation which ultimately with the combing out process of natural selection would probably become comparatively fixed forms or species.

The Northern mandarina-like shell, obviously derived from adusta, is therefore quite distinct from southern typical mandarina, to which species it bears only superficial resemblance; it is accordingly described below as a new sub-species, adusta-mandarinoides, none of the names attributed to the mandarina synonymy being applicable to the northern shell.

Environmental changes in this group evidently take considerable time to develop. In the Hauraki Gulf, mandarinoides is unknown, typical adusta ranging from the rocky litoral (Fig. 30) down to the sandy and muddy 20 fathom depths (Fig. 26). From off Cuvier Island in 36–40 fathoms, slightly modified forms of adusta (Fig. 27) are found, always with the axial sculpture and periphery angle fairly prominent. From Mercury Islands in 40–45 fathoms down to Whakatane in 40–50 fathoms, however, typical mandarinoides (Fig. 31) is mostly found. Only one specimen, referrable to adusta by the slightly angled periphery, was obtained from off Whakatane in about 30 fathoms (Fig. 28). In the Tauranga littoral mandarinoides is the common form (Fig. 32, 135 mm. × 64 mm.) which is found at certain periods breeding at the rocky Beacon Reef inside Tauranga Harbour. The Bay of Plenty being for the most part sandy, probably the advent of mandarinoides to rocky surroundings is of comparatively recent date, sufficient time not having elapsed to bring adaptive forces into play.

It seems quite evident that mandarinoides is the result of slowly-moving adaptive forces rather than that of spontaneous steps or mutations. These acquired changes, due to environment, appear to become transmittable, and an individual is not sufficiently plastic to be able, during its lifetime, to adapt or revert perceptibly to suit changing conditions. Consequently the association of adusta with