The Genetic Relationships of Australasian Rissoids. Part 1. Descriptions of New Recent Genera and Species from New Zealand and Kermadec Islands.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 57, 1927, Page 534

The Genetic Relationships of Australasian Rissoids. Part 1. Descriptions of New Recent Genera and Species from New Zealand and Kermadec Islands. By A. W. B. Powell. [Read before the Auckland Institute, 24 November, 1925; received by Editor, 11th December, 1925; issued separately, 1st February, 1927.] Plates 26–28. Prior to Iredale's (1914-15) Commentary, the Australasian Rissoids, prejudiced by their small size and infinite variety of design, were, with a few exceptions, lumped in a conventional manner in the genus Rissoa, of world-wide range, comprising species of very diverse origin. Iredale, in the above-mentioned paper, proposed eight new genera to cover Australasian forms and utilized five previously described, of which only two were proposed for southern shells. His new genera were, however, quickly adopted by Australasian systematists, the classification being recognized as a decided advance. Finlay, in a valuable paper entitled “N.Z. Tertiary Rissoids” (1924, p. 483), proposed still another genus, but the majority of his new species were easily and naturally located by means of Iredale's new series of genera. In the present paper sixteen new species are described, ten of which fall into previously described genera. In order, however, correctly to express the remaining six species, it has been found necessary to propose five new genera. Some of these new genera are, however, represented in other parts of Australasia by species that have hitherto been ascribed to other groups. If a genus is represented by only one group of undoubted genetic affinity, it should be kept so and not forced to contain species only superficially similar. If several of these aberrant forms themselves resolve into a compact group, it is, in the opinion of the writer, sufficient justification to warrant their generic separation, even on shell characters, where morphological evidence is unavailable. Then these naturally-compiled genera based on evolutionary lines become of great importance to the geologist for the purpose of discussing geographical distribution and geological correlation. It may be argued that this system unnecessarily complicates the nomenclature and that there is a danger of creating almost as many genera as species, but, on the other hand, there is little doubt that only a very small percentage of the New Zealand Rissoid fauna is known, and that further collecting will swell the ranks of these at present poorly represented types. Including the additions recently made by Iredale and Finlay and those described in this paper, the N.Z. Rissoid fauna now numbers sixty-nine species, representing twenty genera. Probably all these species are restricted to New Zealand, many being extremely local. Most of the genera are represented in either south-eastern Australia, Tasmania, or Kermadec Islands, but are not found elsewhere, and show little connection with the northern hemisphere series. Rissoina

seems to be the only widely-distributed genus at present located in the Rissoids, but probably the affinity to the Rissoids is not so close as shell characters indicate. Acknowledgments.—The writer is indebted to Mr. W. A. La Roche and Mr. R. A. Falla for dredgings and samples of shell-sand, and to Mr. G. Archey for permission to sort and describe new species from a Kermadec Islands dredging contained in the Auckland Museum collections. Key to genera grouped around Merelina with diagram showing suggested ancestry. Genus Time, range and recent distribution Protoconch Peristome Adult Sculpture Lironoba Type L. suteri (Hedley) Miocene—Recent Southern N.Z. Tasmania and s.e. Australia A. Smooth (Typical) or B. Spirally lirate Continuous; variced; with sub-sutural sinus Spiral Keels Linemera Type L. interrupta (Finlay) Miocene—Recent Northern N.Z. Tasmania and s.e. Australia Smooth Continuous; thin; with sub-sutural sinus Clathrate Merelina Type M. cheilostoma (T. Wds.) Recent Throughout N.Z. Snares & Bounty Is. Kermadec Is. Tasmania, s e. Australia and Loyalty Is. Spirally lirate Continuous; variced; with sub-sutural sinus Clathrate Vindex Type V. neozelanica (Suter) Recent New Zealand 4 Spiral Keels Discontinuous; thin; not expanded Clathrate strong spirals, weak axials Larochella n g. Type L. toreuma n.sp. Recent North Is. N.Z. Axially ribbed, crossed by faint spiral striæ Discontinuous; thin; expanded; sinuous Heavy rounded spiral keels, axially ribbed. The whole shell with dense spiral striæ Anabathron Type A. contabulatum (Frfld.) Recent Snares Is., N.Z., s e. Australia, New Caledonia. Spirally striate Continuous; variced. Spiral keels with axial foliations Promerelina Type P. crosseaformis (Powell) Recent Northern N.Z. Granular spiral lines Continuous; variced; with sub-sutural sinus; free columella Clathrate or with axials obsolete Awanuia n.g. Type A. dilatata n.sp. Recent Northern N Z. 3 spiral keels Continuous as a callus; thin, expanded; with sub-sutural sinus Strong axial

Lironoba and Linemera are the two oldest genera in the above series, both ranging from Awamoan (Miocene) to Recent. The genotype of Lironoba, the Recent New Zealand suteri, has a smooth protoconch while the two fossil species polyvincta Finlay and charassa Finlay have, in common with the Recent south-eastern Australian wilsonensis Gat. & Gab. a spirally lirate nucleus, although agreeing perfectly with the genotype in all adult characters. Finlay (1924, p. 486), however, considers the New Zealand Miocene polyvincta, Pliocene charassa, and Recent suteri an evolutionary series. Thus, in Lironoba, contrary to other Rissoids, the nuclear characters seem variable. No genera proposed or adopted in this paper, however, are based on nuclear variation only, adult sculpture and type of aperture being also taken into consideration. Although the Recent New Zealand Rissoids had, until quite lately, been given little attention, still less has been given to fossil species, Finlay's paper on the New Zealand Tertiary species being the first reliable census. The number of known fossil genera and species must not, therefore, be considered representative. No doubt the widely-distributed Recent Merelina will yet be found fossil associated with Lironoba and Linemera, both of which also share a wide recent Australasian distribution. Merelina Of the three species of Merelina described below, superba is the nearest to the genotype; gemmata is related to australiae (Frauenfeld), both having a depressed protoconch, sculptured with three spirals only, while compacta has a similarly-shaped nucleus with more numerous spirals, but not so many as in genotype. Although differing slightly in apical features, the apertures in all above-mentioned species show no variation from genotype. The nuclear sculpture in Merelina is always in form of plain spirals, not granulated as in the related genus Promerelina proposed by writer (1926, p. 593) for two species, each with a remarkable large basal ridge and free columbella in addition to the apical difference. Merelina superba n. sp. (Fig. 2). Shell small, solid, clathrate. Protoconch typical, spirally striate of of 1½ convex papillate whorls, sculptured with ten spiral striae.

Whorls 6½. Suture narrowly but distinctly margined. Sculpture consisting of strong spirals crossed by stronger axials, slightly nodulus at points of intersection. First post-nuclear whorl with two spirals, following three developing a third rib and body-whorl with four, plus an inconspicuous sub-sutural fifth and three on base. Axials strong, reaching from suture to suture, but not extending over base, enclosing where they cross the spirals, horizontal rectangular spaces. Aperture typical, thickened with a varix, peristome continuous, double with a slight indentation above, near suture. Colour buff, banded just below suture and coloured on base with light brown. Height, 3.6 mm.; diameter, 1.4 mm. Holotype in author's collection, Auckland. Habitat: Maro Tiri (Chicken Island (type) in shell sand. (Coll. R. Falla, Dec., 1923); Mangonui in 6–10 fathoms (one specimen from dredgings by W. La Roche, June, 1924). Distinguished from the related Australian gracilis (Angas) and cheilostoma (Ten.-Woods) by the greater number of spiral keels and consequent difference in outline. Merelina gemmata n. sp. (Fig. 1). Shell small, solid, clathrate. Protoconch depressed dome shaped of 1½ whorls sculptured with three spirals. Whorls 5½. Sculpture consisting of strong spirals crossed by strong broad axials rendered nodulus at points of intersection. Post-nuclear whorls with three spirals, the lower two more prominent, body-whorl developing four plus two on base. Outlines roughly oval, very little indented at sutures. Aperture typical, thickened with a varix, peristome continuous, double with a slight indentation above, near suture. Colour white, shining. Height, 2.9 mm.; diameter, 1.25 mm. Holotype in author's collection, Auckland. Habitat: Maro Tiri (Chicken Island (type) and four paratypes in shell sand (Coll. R. Falla, Dec., 1923); Taupo Bay, Whangaroa (1 sp. collected by W. La Roche). This species is closely related to the Australian M. australiae (Frauenfeld) which has a similar paucispiral protoconch but has 1 whorl less than gemmata, an extra spiral on body-whorl is proportionately broader and a smaller shell. Merelina compacta n. sp. (Figs. 5, 5a). Shell minute, solid, clathrate. Protoconch large depressed, rounded of 1¾ whorls sculptured with 6 spirals. Whorls 4. Suture narrowly margined. Sculpture consisting of heavy rounded spirals crossed by regularly-spaced stronger axials extending from suture to suture and over base. First two post-nuclear whorls sculptured with two spirals, body-whorl with three, the upper two strongest, plus three more on base. Although heavy and prominent the sculpture does not enclose sharply outlined rectangular spaces. Aperture typical thickened, with a varix, peristome continuous, double, with a slight indentation above, near suture. Colour uniformly buff. Height, 1.35 mm.; diameter, 0.65 mm. Holotype in author's collection, Auckland.

Habitat: Mangonui in 6–10 fathoms (holotype and 1 paratype from dredgings by Mr. W. La Roche, June, 1924). Differs from the cheilostoma, typical series, in the relatively larger and depressed form of the protoconch, with fewer striations. Merelina pisinna (Melvill Standcn) (Fig. 11). Alvania pisinna Melv. & Stand., Journ. Conch., 8 (1896) 305. A figure is provided of the species recorded as above from 10–30 metres near Sunday Id., Kermadec Is. (Oliver, 1915, p. 519), in order to illustrate the curious straight-sided protoconch. The type is from the Loyalty Is., so when specimens from both localities are critically compared the Kermadec shells may prove distinct. Rissoids have two main types of apertures according to environment. Shells living under stones, in sand, and in shingle, formed to withstand its battering action are solidly built with thickened, often variced apertures, while those always found clinging fast to the protecting fronds of seaweeds are much more fragile, having thin, often expanded apertures. The heavily variced Merelina and Promerelina are found either under stones, in shell-sand, or in dredgings. The species described below, having apical features somewhat similar to Merelina, but a thin expanded lip shows apparent evolution of a distinct genus due to change of environment. Although all available specimens were dead shells from shallow-water dredgings and shell-sand, most of the associated species were typical seaweed-frequenting species, indicating its true station in life. That these adapted forms continue to breed true to their acquired structural changes is evident by the series collected, thus showing their right to be considered distinct from the series they branched off from. The environmental change, necessarily extreme to bring about so sudden a change; also indicates the improbability of the existence of intermediate forms, thus the two series continue to flourish apart. Awanuia n. gen. Type: Awanuia dilatata, Powell. Protoconch large, depressed, rounded, sculptured with 3 spiral ridges. Strong axial ribs on all post-nuclear whorls. Peristome thin, continuous as a callus across parietal wall, widely expanded on free portion of lip, with a distinct, broad, shallow sinus between suture and shoulder, being much more pronounced than in Merelina. Peristome strengthened with fine radiating riblets, quite the reverse to the concentrically thickened, variced, outer lip of Merelina. In addition to the distinctive mouth-characters, Awanuia differs from Merelina in adult sculpture which consists of axials only, with exception of first post-nuclear whorl, on which, in addition to axials, are two faintly indicated spiral threads, sufficient, in conjunction with the spirally ribbed protoconch to show the ancestral relationship to Merelina. The genus Larochella also described in this paper is still another example of a Rissoid with this type of aperture, adapted for a life on seaweeds.

Awanuia dilatata n. sp. (Fig. 3). Shell minute, thin, white. Protoconch large, depressed, rounded of 1½ whorls, sculptured with three spiral ridges. Whorls 4½, with flattened sides sharply angled above and at periphery. Shoulder slightly concave. Base smooth. Sculpture on all post-nuclear whorls consisting of prominent axial ribs crossed on the first post-nuclear only by two faintly-indicated spiral threads. Peristome thin, continuous as a callus across parietal wall, widely expanded on free portion of lip, strengthened on the inside by faint radiating riblets and with a broad distinct, shallow sinus above, between suture and shoulder. Height, 1.5 mm.; diameter, 0.8 mm. Holotypes and paratypes in author's collection, Auckland, also paratypes in Auckland and Dominion Museums. Habitat: Awanui (or Rangaunu Bay) in twelve fathoms. Mangonui in 6–10 fathoms (type); many dead shells from dredgings by W. La Roche. For Mathilda neozelanica Suter and Alics succincta Suter, Iredale and Finlay have proposed a new genus Vindex, citing the former species as type and provisionally locating the genus near Lironoba. The protoconch is sculptured with four spiral keels, the adult whorls being also heavily keeled, crossed by weak axials, while the peristome is thin and discontinuous. Larochella n. gen. Type: Larochella toreuma Powell. The above new genus is proposed for the two species described below, the protoconch being sculptured with strong regularly-spaced axial ribs, crossed by numerous fine spiral lirae. Although these shells recall Vindex in shape and general appearance, the nuclear characters are quite dissimilar, as also is the adult type of sculpture and aperture. Adult sculpture consists of heavy rounded keels, crossed on the keels only by prominent axial ribs, while the whole shell is crowded with numerous fine spiral lirae. Peristome thin, slightly expanded where free and connected as a thin callus across parietal wall. Outer lip sinuous, indented corresponding to the termination of the interstices of the keels. The type of aperture in this genus, as in Awanuia, indicates a structural change to suit environment. No doubt the seaweed-frequenting Larochella has evolved from Vindex of sandy and deep water habitat, for, in addition to the changed peristome, Larochella shows gradual evolution from Vindex by a more complex sculptural nucleus. Genus named in honour of Mr. W. La Roche, of Auckland, whose extensive collection and dredging has resulted in many new species, genera, and records being added to the New Zealand fauna. Known distribution North Island of New Zealand. Vindex succincta (Suter) is so far, known only from southern New Zealand. Odhner's record from Colville Channel in 35 fathoms refers to juvenile Turritella vittata Hutton, as shown by specimens received from recorder.

Larochella toreuma n. sp. (Fig. 4). Shell minute, thin, white. Protoconch large dome-shaped, with nucleus slightly oblique of 1½ convex, axially-ribbed whorls crossed by numerous fine spiral lirae. Axials and their interstices of about equal width. Whorls 5½. Sculpture on all post-nuclear whorls consisting of three prominent rounded keels, the middle one by far the strongest. Keels only crossed by regularly spaced axials. All whorls crowded with fine spiral lirae. Peristome thin, slightly expanded where free and connected as a thin callus across parietal wall. Outer lip sinuous, being indented above and below, corresponding to the termination of the interstices of the keels. Height, 1.25 mm.; diameter, 0.5 mm. Holotype and one paratype in author's collection, Auckland. Habitat: Houghton Bay, Cook Strait (seaweed-washings) A. W. B. P., May. 1925. Larochella alta n. sp. (Fig. 6). Shell minute, thin, white. Protoconch large, depressed, rounded, of 1½ convex axially ribbed whorls crossed by numerous fine spiral lirae. Interstices of axials equal to about 1½ times width of axials. Whorls 6½. Two heavy spiral keels on spire-whorls, the lower one much the stronger. On body-whorl a third keel equal in strength to the upper one proceeds from suture. Details of sculpture on all whorls as in foregoing species. Peristome thin, sinuous and identical with that of toreuma. Height, 1.6 mm.; diameter, 0.6 mm. Holotype and many paratypes in author's collection, Auckland. Paratypes also in Auckland, Dominion and Canterbury Museums. Habitat: Mangonui in 6–10 fathoms (type) Awanui (or Rangaunu Bay) in twelve fathoms. (Many dead shells from dredgings by Mr. W. La Roche.) From toreuma, alta differs in having a proportionately-smaller protoconch with wider spaced axials, one more adult whorl and only two keels showing on spire whorls. The main keel is also proportionately much stronger, giving the shell much more indented outlines. Onoba Iredale, in his 1915 Commentary, p. 449, placed Webster's Rissou candidissima and R. carnosa in the genus Onoba H. & A. Adams, and remarked that both species accurately agreed with striata Montagu, an English shell and genotype of Onoba. In the same paper, p. 450, he proposed Subonoba with R. fumata Suter, as type for a series of New Zealand shells, spirally grooved similarly to Onoba, but minus axials, semitransparent, no colour markings, and having a thin continuous peristome. The genotype of Onoba is a tapering shell, spirally grooved, colour banded, with weak axials, a small protoconch and a discontinuous peristome, constricted above. Carnosa and candidissima only superficially resemble the English Onoba, the protoconch being proportionately much larger and in adult specimens the peristome continuous as a heavy callus.

Webster (1905, p. 278) gives dimensions of carnosa as 2.25 mm. × 0.75 mm. His enlarged figure, however, measures 32.5 mm. × 16.5 discontinuous peristome. In adult topotypes, of which one is figured was not the one described, but a juvenile, which accounts for the different proportion, axials extending strongly over body-whorl and discontinuous peristome. In adult topotypes, of which one is figured (Fig. 7), axials are less conspicuous on the last whorl and do not extend below periphery. Suter (p. 222) gives dimensions as 3 mm. × 1.3 mm., but the writer has not seen any so large. For the New Zealand and Kermadec Island shells hitherto recorded as Onoba, but differing from that genus in particulars mentioned above, a new genus, Austronoba, is proposed with Webster's candidissima as type, and to include carnosa Webster, kermadecensis nov and oliveri nov. The genotype and allied kermadecensis nov. are always white, but carnosa and its evolutionary product oliveri nov. are coloured. This is not a constant feature, however, a few of Oliveri being white, but every intermediate form occurs between it and uniform brown and banded shells. I have not seen white carnosa, but uniformly brown shells are as common as the typical banded ones candidissima resembles Subonoba by the absence of coloration and in having spiral sculpture and similar apical characters, but the presence of strong axials on all post-nuclear whorls separates it from that genus, which is always devoid of axials. Iredale (1924, p. 244) proposed a new genus, Botellus, for Hedley's South Australian O. bassiana (type) and Queensland O. glomerosa, differing from typical Onoba Austronoba nov., and Subonoba, in being thick heavy shells with circular thickened apertures. The known distribution of Austronoba is Northern New Zealand and Kermadec Island, of Botellus South Australis, Tasmania, and Queensland, and of Subonoba, throughout New Zealand and in the Antarctic. Austronoba seems more closely related to Subonoba than to the Australian Botellus, thus showing a southern origin for the genus with no indications of a connection with Onoba of the northern hemisphere. Austronoba n. gen. Type: Rissoa candidissima Webster. Shell thin, semitransparent, white, uniformly coloured or banded. Dense spiral sculpture crossed by prominent axials; protoconch smooth, dome-shaped; aperture ovate-pyriform, peristome thin continuous as a callus across parietal wall, not varicose. Austronoba candidissima (Webster) (Fig. 12). Webster's figure of this species does not show the essential characters, so a specimen is figured (1.9 mm. × 0.8 mm.) collected together with one other at Tryphena Bay, Great Barrier Island (Jan., 1924), from under-side of stone at low tide. Later, Mr. W. La Roche collected a single specimen from a similar station at Taupo Bay, Whangaroa. Webster's type was from Takapuna and measured 2 mm × 1 mm.

Austronoba kermadecensis n. sp. (Fig. 8). Shell minute, thin but not fragile, semitransparent, white. Protoconch large, dome-shaped, of two smooth whorls. Whorls five. Sculpture consisting of numerous narrowly rounded spirals crossed by distant slightly oblique axial ribs not extending below periphery. Peristome continuous as a heavy callus across parietal wall, outer lip not varicose. From candidissima, kermadecensis differs in having a greater number of spirals, sixteen narrowly rounded spirals on body-whorl as compared with the twelve broad spirals of the first-named species. The diameter is also greater in proportion to height than in candidissima. Both Webster and Suter wrongly described the peristome of can-didissima as being discontinuous for it is exactly the same type as described in kermadecensis nov. and typical of the other species of Austronoba. Height, 1.76 mm.; diameter, 0.9 mm. Type in Auckland Museum. Holotype and many paratypes, all dead shells 10–30 metres off Sunday Id., Kermadec Is. (from dredgings in Auckland Museum, by R. S. Bell). In ascribing carnosa to the Kermadec fauna, Oliver named four colour-varieties, typica, fusca, alba, and bicolor. No types, however, were designated, as his names were intended only to indicate colour-forms. Furthermore, the names were applied to a New Zealand shell, not really a constituent of the Kermadec fauna as shown below. The first name, typica, simply means carnosa typical, so cannot be used for the Kermadec shell, and the remaining colour-forms are not constantly distinct, so in the event of one of the names being raised to specific status, the others would fall as synonyms. As it is quite obvious that the names were not intended in a subspecific sense, but merely to indicate colour-forms, the proper course seems to be to employ an entirely new name for the Kermadec shell. Austronoba oliveri n. sp. (Fig. 9). Shell minute, thin, but not fragile, colour variable, entirely white or with the early whorls reddish brown, entirely brown, or with a broad white band above periphery. Protoconch large dome-shaped of two smooth whorls. Whorls five. Outlines convex, whorls slightly angled at periphery. Sculpture consisting of about twenty-five fine spiral riblets crossed by oblique axial costae about twenty on last whorl, stronger on spire than on body-whorl and not extending below periphery. Peristome continuous as a heavy callus across parietal wall, outer lip not varicose. From carnosa, its closest ally, oliveri differs in the contour of the body-whorl, being noticeably more convex and slightly angled, with periphery high on the body-whorl and more numerous spirals. Carnosa has the whorls only slightly convex and the periphery angle much lower. In the large series examined these features are quite constant, the colour alone being variable. Height, 2.25 mm.; diameter, 0.9 mm. Type in Auckland Museum.

Holotype and many paratypes, all dead shells, from 10–30 metres off Sunday Id., Kermadec Is. (from dredgings by R. S. Bell) in Auckland Museum. Both this species and kermadecensis nov. have evolved from the New Zealand species carnosa and candidissima respectively, to which two species the Kermadec shells had hitherto been ascribed. Rissoa cylindrella Odhner (1924, p. 22, Pl. 1, f. 14), although similar superficially to Austronoba, cannot be included here on account of the spirally-striated protoconch indicating quite a different group. Until actual specimens are available, however, the exact position of this species must remain in doubt. Estea Iredale (1915). (Trans. N.Z. Inst., 47, 451). Estea semiplicata n. sp. (Fig. 17). Shell of moderate size, solid, imperforate, protoconch domeshaped of 1½ smooth whorls. Whorls 5½, spire conic, outlines almost straight, angled at periphery. Sculpture, smooth to the fourth whorl, then for a space equal to one whorl, strong axial plications suddenly develop and then disappear on last half-whorl. Plications extending from suture to suture, but not extending over base. Suture impressed, aperture almost circular, peristome continuous, edge thin and reflexed but internally thickened. Colour buff with a dark reddish-brown band on lower half of whorls but not extending below periphery. Height, 2.5 mm.; diameter, 1.25 mm. Holotype and paratypes in author's collection, Auckland. Habitat: Taupo Bay, Whangaroa (type) coll. W. La Roche; Mangonui Heads; Tryphena Bay, Great Barrier Id. on under sides of stones at low tide (coll. A. W. B. P., 1924). This species is slightly larger than E. zosterophila and is easily distinguished from it by presence of the axial folds, which are quite a constant feature, as indicated in the large series examined from several localities. In other respects, however, in coloration, shape, and form of aperture, semiplicata shows close relationship to zosterophila and is no doubt an evolutionary product of that species. Estea angustata n. sp. (Fig. 10). Shell very small, rather thin. Protoconch dome-shaped of 1½ smooth whorls. Whorls 4½, smooth, spire tall, cylindrical, 2¼ times height of aperture, sides straight and parallel. Suture impressed, with an infrasutural groove below. Aperture typical, peristome continuous, thin, reflexed all round and internally thickened. Colour reddish-brown, lighter on body-whorl with a narrow dark-brown band at periphery, peristome white. Height, 1.7 mm.; diameter, 0.5 mm. Holotype in author's collection, Auckland. Habitat: Mangonui in 6–10 fathoms (a few specimens from dredgings by W. La Roche). A very distinctive species characteristic of Estea but not closely related to any other known species.

Estea, ranging from Pliocene to Recent, is rather rich in species. Typical Estea, which is a solid opaque shell, has an almost circular aperture with a thin peristome, reflexed all round and joined to parietal wall only for a short space. The adult whorls may be smooth, ornamented with axial growth-lines, folds, or riblets, or spirally lirate sometimes with combined axial and spiral sculpture. This latter combination, however, seems to be confined to a few Pliocene species, the spirals being indicated as a recessive character absent in all Recent examples, excepting the occasional occurrence in some axially-costate species of a single infrasutural groove. Striatestea n. gen. Type: S. bountyensis Powell. The species described below, together with the Victorian janjucensis Gat. & Gab., and iravadioides Gat. & Gab., all here referred to above new genus, form a compact group only superficially reminiscent of Estea, to which genus the two Victorian species had previously been ascribed. Compared with Estea, Striatestea has a totally different type of aperture, is devoid of axial sculpture and is a much thinner and more fragile shell. Shell small, tall, elongate-conic, thin, semitransparent, white. Protoconch small, smooth, conical. Adult whorls smooth to spirally ribbed or grooved. Aperture continuous, almost pyriform, constricted above and rounded below, thin and reflexed where free, but joined to body-whorl for whole extent of inner lip, which is marked off from body-whorl by a slight groove. Outer lip straight with axis of whorls, not retracted towards suture as in Subonoba and Austronoba. Considering the comparatively wide range of this group in conjunction with such distinctive and constant shell-characters, the writer has no hesitation in proposing a new genus for the group. A single worn shell from Stewart Island, in shell sand, closely related to bountyensis, is withheld from description pending receipt of better material. Further collecting will, no doubt, disclose many other examples from intermediate localities. Striatestea bountyensis n. sp. (Fig. 18). Shell small, thin, semitransparent, white. Protoconch small, smooth conical of one whorl. Whorls four. Spire tall, twice height of aperture, outlines slightly convex. Suture impressed, faintly and narrowly margined. Sculpture, spire whorls smooth, base with three strong spiral ribs. Aperture continuous, almost pyriform, constricted above, rounded below, thin and reflexed where free, but joined to body-whorl for whole extent of inner lip, which is marked off from body-whorl by slight groove, inner lip very little curved but forming an acute angle above with outer lip. Height, 1.4 mm.; diameter, 0.6 mm. Holotype in author's collection, Auckland. Habitat: South of Bounty Island in 170 fathoms (one sp. from dredgings by Capt. Fairchild, 1893).

Fig. 1.—Merelina gemmata n.sp. Fig. 2.—Merelina superba n.sp. Fig. 3.—Awanuia dilatata n.sp. Fig. 4.—Larochella toreuma n.sp. Figs. 5 & 5a.—Merelina compacta n.sp. Fig. 6.—Larochella alta n.sp.

Fig. 7.—Austronoba carnosa (Webster). Fig. 8.—Austronoba kermadecensis n.sp. Fig. 9.—Austronoba oliveri n.sp. Fig. 10.—Estea angustata n.sp. Fig. 11.—Merelina pisinna (Melv. & Stand.) Fig. 12.—Austronoba candidissima (Webster).

Fig. 13.—Scrobs hedleyi (Suter). Fig. 14.—Scrobs elongata n.sp. Fig. 15.—Scrobs hedleyi angulata n.subsp. Fig. 16.—Epigrus striatus n.sp. Fig. 17.—Estea semiplicata n.sp. Fig. 18.—Striatestea bountyensis n.sp. Fig. 19.—Notoscrobs ornata n.sp. Fig. 20.—Scrobs ovata n.sp.

The associated material, however, contained many shallow water forms, such as Gaimardia and Acmaea. Probably the bulk of the material originated in shallow water, but was transported to greater depths by currents. Epigrus Hedley (Mem. Austr. Mus. (1903) 355) Epigrus striatus n. sp. (Fig. 16). Shell minute, elongate-oval, solid. Protoconch smooth, of 1½ whorls. Whorls 4½ slightly convex, very finely spirally striated. Suture canaliculate with an infrasutural groove below. Spire twice height of aperture. Aperture oblique, oval, extended slightly beyond body-whorl and separated from it by a deep groove. Peristome very thick and rounded. Colour white. Height, 1.5 mm.; diameter, 0.6 mm. Holotype and one paratype in author's collection, Auckland. Habitat: Mangonui in 6–10 fathoms (from dredgings by W. La Roche). The genus has not previously been recorded Recent from New Zealand, but is known fossil from Pukeuri (Miocene) represented by a single fragmentary specimen (Finlay, 1924, p. 489). This species fossilis is described as having no sculpture excepting fine growth-lines, and is a larger shell than striatus. Epigrus is also known Recent from the Kermadec Islands, Tasmania and s.-e. Australia. Scrobs Watson “Challenger” Zoology 15 p. (1886) 612 Type: S. jacksoni (Brazier)—Rissoa (Scrobs) badia Watson—Amphithalamus Carpenter (of Australasian Authors). Iredale, in his 1915 Commentary, p. 449, wrote, “Amphithalamus is a name I have a great dislike to as it was given to a North American species, and the Austral species so called have an Austral name already available.” This name is Scrobs, which is here adopted in preference to Amphithalamus for Australasian usage. The resemblance of the Austral shells to Amphithalamus is merely superficial, prejudiced by the presence of a depression sparating aperture from body-whorl. In nuclear characters Scrobs is quite unlike Amphithalamus, this latter genus having protoconch sculptured with about fifteen slender spiral threads crossed by numerous very fine axial threads, giving the surface a minutely pitted appearance, while in Scroba the nuclear sculpture is in the form of numerous very fine stippled lines. Key to Scrobs Groups. A. Shell solid, ovate; apertue separated from body-whorl by sunken space: (a) Adult whorls, smooth. (Typical). 1. S. jacksoni (Brazier)—S.-e. Australia, Tasmania. 2. S. luteofuscus (May)—Tasmania. 3. S. sundayensis (Oliver)—Kermadec Islands. (b) Adult whorls spirally striate or spirally keeled. 4. S. ovata n.sp.—Northern New Zealand. 5. S. hedleyi (Suter)—New Zealand. 6. S. hedleyi var. angulata n. sub. sp.—Northern New Zealand.

B. Shell solid, slender, adult whorls with a few spirals on base; aperture not separated from body-whorl by sunken space but a slight groove in a shallow depression marks off inner lip from body-whorl. 7. S. scrobiculator (Watson)—S.-e. Australia. 8. S. petterdi (Brazier)—S.e. Australia, Tasmania. 9. S. elongata n.sp.—Northern New Zealand. C. Shell solid, spire tall, conic; adult whorls with a peripheral groove; aperture separated from body-whorl by a slight cleft. 10. S. semen (Odhner)—North Island, New Zealand. Scrobs ovata n. sp. (Fig. 20). Shell minute, solid, ovate. Protoconch of 1½ globose whorls sculptured with numerous fine stippled lines. Whorls 3½. Adult whorls smooth excepting a few spiral grooves on base. Suture distinctly margined. Aperture oblique oval, much thickened, and separated from body-whorl by a broad sunken callosity. Peristome continuous, double, the outer lip continuing over depression and joining body-whorl. Colour light reddish-brown, paler on base, with colourless peristome. Dead shells whitish, semitransparent. Height, 1 mm.; diameter, 0.5 mm. Holotype in author's collection, Auckland. Paratypes in Auck land, Dominion and Christchurch Museums. Habitat: Awanui (or Rangaunu Bay) in twelve fathoms (type); Mangonui in 6–10 fathoms (from dredgings by W. La Roche). Scrobs hedleyi (Suter) (Fig. 13). Suter incorrectly described the protoconch of this species as being of one flatly convex smooth whorl. The nucleus is, however, typical of Scrobs, sculptured with the numerous fine stippled lines, and is large, dome-shaped, of 1½ whorls. His figure likewise does not correctly represent the species, so a figure of a topotype is provided. Height, 1.2 mm.; diameter, 0.7 mm. Scrobs hedleyi angulata n. subsp. (Fig. 15). Shell differing from the species in shape and details of sculpture. The diameter, compared with that of hedleyi, is proportionately greater and the spiral keels are much more prominent, causing a sharp angle on the outer lip. The third keel shown in figure may be pronounced or only faintly indicated as a slight angle. Colour reddish-brown, lighter towards base, with aperture white, or the whole shell white. Similar to species in all other respects. Height, 0.9 mm.; diameter, 0.6 mm. Holotype in author's collection, Auckland. Habitat: Mangonui in 6–10 fathoms (from dredgings by W. La Roche). Both species and subspecies were found in this dredging, the latter predominating in number. A series of about thirty specimens was examined and, although variable, both kinds were well characterized and easily separable.

Scrobs elongata n. sp. (Fig. 14). Shell minute, cylindrical, very solid, adult whorls smooth. Protoconch of two globose whorls, sculptured with numerous fine stippled lines. Whorls four, slightly convex. Suture distinctly margined. Aperture oblique, oval, much thickened with continuous double peristome, smooth inside, but surrounded with a broad, unevenly striated thickened area, widest on the inner lip, where it slopes towards the parietal wall, being marked off from it by a shallow groove. A slight fold proceeds from the base for a short distance on body-whorl, parallel with inner lip. The groove marks the bottom of a V shaped depression between the inner lip and basal fold. Colour light reddish-brown, paler on base, with colourless peristome. Dead shells whitish, semitransparent. Height, 1.1 mm.; diameter, 0.45 mm. Holotype in author's collection, Auckland. Paratypes in Auckland, Dominion and Christchurch Museums. Habital: Awanui (or Rangaunu Bay) in twelve fathoms (type); Mangonui in 6–10 fathoms (from dredgings by W. La Roche). Scrobs semem (Odhner) Papers from Dr. Th. Mortensen's Pacific Exp., 1914–16, 19, N.Z. Mollusca, p. 22, pl. 1, figs. 10, 11, 1924. This species, described by Odhner as a Rissoa, is undoubtedly a Scrobs. Specimens agreeing exactly with R. semem, which is from Cape Maria van Diemen (on seaweeds) were recently collected by the writer at Houghton Bay, Cook Strait, also from seaweed-washings. R. semem has a peripheral groove and other strong superficial resemblances to the s.-e. Australian incidata Frauenfeld, which Hedley, May, and Iredale have unhesitatingly located under Estea; but Estea has a smooth nucleus, while in Scrobs the protoconch is sculptured with numerous fine stippled lines. The Cook Strait specimens undoubtedly represent Suter's New Zealand record of incidata, but, as they agree with Scrobs semem, they cannot equal Estea incidata unless the latter has been incorrectly described. The nuclear sculpture of Scrobs, however, is so fine that the slightest erosion would efface it, when species of this group of Scrobs would certainly resemble Estea, especially as the aperture is not noticeably separated from body-whorl as in typical Scrobs. Rissoid species, being usually of restricted distribution, however, it is convenient to use Odhner's name for the New Zealand “incidata” until topotypes of both species are compared. Notoscrobs n. gen. Type: Notoscrobs ornata Powell. The new species described below makes the third known example of a well defined group of Scrobs origin, but too dissimilar to form a natural association with the species of that genus. One of the species is from Tasmania and the remaining two from New Zealand, indicating in addition to the distinctive shell-characters that the genus is by no means of recent development.

Comparative Key to Both Genera: Scrobs: Shell solid, ovate, protoconch large dome-shaped, sculptured with numerous very fine stippled lines, adult whorls smooth, spirally striate or spirally keeled; aperture extending beyond body-whorl and separated from it by a sunken space, peristome continuous duplicated. Notoscrobs: Shell solid, conical; protoconch large dome-shaped, sculptured with about 12 spiral rows of round shallow pits which, as they do not also form vertical rows produce a honeycomb effect, adult whorls with plain spiral keels, the uppermost crossed by axial ribs; aperture not separated from body-whorl, peristome continuous, duplicated, inner margin smooth and narrow surrounded by a broad flattened area, widest above and on parietal wall. Notoscrobs ornata n. sp. (Fig. 19). Shell minute, solid, conical, imperforate. Protoconch domeshaped, of 1½ whorls, sculptured with about twelve spiral rows of minute round shallow pits spaced alternate with those of rows immediately above and below, giving a honeycomb effect. Whorls 4½. Spire conic, outlines straight. Spire-whorls sculptured with two spiral keels, the upper one crossed by slightly oblique strong axial ribs, last whorl plus three plain spiral keels on base. Aperture oblique, oval, slightly constricted above, peristome duplicated, continuous with a smooth raised inner margin surrounded by an expanded slightly concave area, widest above and on parietal wall with its outer edge bounded by a slight ridge. Colour light reddish-brown, darker on keels. Height, 1.3 mm.; diameter, 0.8 mm. Holotype and several paratypes in author's collection, Auckland. Habitat: Mangonui Heads in 5–6 fathoms (type) (from dredgings by W. La Roche, 1924); Maro Tiri (Chicken Island) in shell sand (coll. R. A. Falla, Dec., 1923). Amphithalamus triangulus May (p. 95, Pl. 6, f. 32, 1915), and Rissoa erosa Odhner (p. 23, pl. 1, figs. 12, 13, 1924) both belong to Notoscrobs. Literature Cited. Finlay, H. J., 1924. N.Z. Tertiary Rissoids, Trans. N.Z. Inst., vol. 55, pp. 480–494. Hedley, C., 1918. A check-list of the Marine Fauna of N.S.W., Pt. 1, Mollusca, Pro. Roy. Soc. N.S.W., vol. 51, pp. 52–54. Iredale, T., 1915. A commentary on Suter's Manual of the N.Z. Mollusca, Trans. N.Z. Inst., vol. 47, pp. 447–454. — 1924. Results from Roy Bell's Molluscan Collections, Pro. Linn. Soc. N.S.W., 49, pt. 3, p. 244. May, W. L., 1915. Additions to the Tasmanian Marine Mollusca with descriptions of the New Species, Pro. Roy. Soc. Tasmania. — 1921. A check list of the Mollusca of Tasmania, pp. 49–53. — 1923. W. L. May's Illustrated Index of Tasmanian Shells, pp. 50–53. Odhner, N. H., 1924. Papers from Dr. Th. Mortensen's Pacific Expedition, 1914–16, 19, New Zealand Mollusca. Oliver, W. R. B., 1915. The Mollusca of the Kermadec Islands, Trans. N.Z. Inst., vol. 47., pp. 519–521. Powell, A. W. B., 1926. Descriptions of Six New Species and a New Genus of Gasteropod Mollusca from Northern New Zealand, Trans. N.Z. Inst., vol. 56, pp. 593–594. Webster, W. H., 1905. On some new Species of Shells, Trans. N.Z. Inst., vol. 37, pp. 276–280.