Art. 36.—Marine Littoral Plant and Animal Communities in New Zealand.

By W. R. B. Oliver, F.L.S., F.Z.S., Dominion Museum, Wellington.

Zealand is a form of Avicennia officinalis, not extending south of latitude 38° S. Animals living a semi-terrestrial existence here are Amphibola crenata, Potamopyrgus antipodum, Phytia ornata, Helice crassa, and certain amphipods. The same forms live in similar situations in salt marshes. But a more direct route over a sandy beach might be taken by such crustacea as Talorchestia quoyana, and others which occur under seaweed cast up during storms. The rocky coast, too, provides a means whereby marine animals can change their habitat for a terrestrial existence. Members of the family Littorinidae provide examples of gasteropod molluscs living in stations reached only by spray from the waves. Unlike the majority of shelled animals between tide-marks, they do not habitually hold water within their shells during the retirement of the tide, but seal themselves up behind their opercula, and attach the peristome of their shells to the rock by means of a mucilaginous secretion. An interesting summary of the habits of Littorinoids in this connection is given by Hedley (1915, p. 33). The New Zealand members of this family, Melaraphe unifasciata and M. cincta, have already been mentioned as advancing up the rocky coast to beyond the lower limit of land vegetation. More success, however, appears to be achieved by gasteropods in crossing the rocky shore where patches of succulent plants are found beyond high-water mark. At Island Bay, Cook Strait, occurs a plant-formation consisting chiefly of a low dense growth of Selliera radicans and Triglochin striatum, where soil has collected in hollows among the rocks well beyond the reach of the tides. By searching carefully among this, Marinula filholi and Acmella neozelanica may be found in abundance. The former, however, is a pulmonate occurring between tide-marks.

Ocean Currents.

The shores of New Zealand are washed by at least two distinct ocean currents. The Antarctic drift current, which has a general set towards the north-east, affects chiefly the southern and eastern coasts as far north as Jackson's Bay on the west and Banks Peninsula on the east. From Jackson's Bay the current flows southward along the coast and through Foveaux Strait. Drift from the south of New Zealand has been cast up on the Chatham Islands; there are certain points of agreement, too, between the fauna and flora of the same two localities. This current appears to be pushed off shore by a current, presently to be described, passing through Cook Strait from the west. The second ocean current reaching New Zealand is probably a continuation of the Notonectian current which, after flowing southward down the east coast of Australia, is diverted eastwards on coming into contact with the Antarctic drift current about the latitude of Tasmania. Crossing the Tasman Sea, it impinges against the west coast of New Zealand, and is again in the main deflected to the northward, and, passing round the northern part of New Zealand, continues in an easterly or south-easterly direction. Winds no doubt cause diversions, in the surface layers at any rate, as logs from northern New Zealand rivers are frequently cast up at the Kermadec Islands. A current passes eastward through Cook Strait, part of it coasting southward to Banks Peninsula and the remainder continuing in a south-easterly direction of shore. The current crossing Tasman Sea possibly has some influence, accounting for the supposed more equable climate on the west coast of New Zealand as compared with the east coast. To the effect of this

current also may be attributed the sundry visitors from the tropics recorded from time to time from the coast of New Zealand north of Raglan and the Bay of Plenty. Among the drift may be mentioned the fruits of Barringtonia, whilst stragglers amongst animals include the green turtle (Chelone mydas), leathery turtle (Dermochelys coriacea), common sea-snake (Hydrus platurus), and ringed sea-snake (Platurus colubrinus). (See Cheeseman, Trans. N.Z. Inst., vol. 40, p. 167.)

Local surface currents on the coast of New Zealand are determined mainly by tides. The flood tide runs eastward through Foveaux Strait and northward along the coast of New Zealand and through Cook Strait. In Hauraki Gulf, however, it flows south. On the west coast of the North Island the flood tide runs south as far as Cape Egmont, with a northerly diversion in Taranaki Bight. Past Cape Campbell it is westerly. Ebb tidal streams are the reverse of these.

Sea-temperature.

There is a considerable difference between the temperature of the sea in the north and in the south of New Zealand. The annual range for each locality, however, is about the same—namely, 8°–9° C. The dependence of the temperature of the surface of the sea on that of the air is well shown by the annexed graph, which is compiled from Anderton's report mentioned below. While the curve of sea-temperature follows that of the air, its amplitude is much less, and the maxima and minima usually follow extremes in the atmosphere.

Diagram showing dependence of sea-temperature (thick line) on air-temperature (thin line), Porfcobello.

I give herewith a table showing air- and sea-temperatures for a period of a year at Auckland, Wellington, and Dunedin. The figures for Auckland were kindly supplied me by Mr. W. H. Hamer, M.Inst.C.B., Engineer to the Auckland Harbour Board. Those for Portobello were taken by Mr. T. Anderton, and recorded in Trans. N.Z. Inst., vol. 38, p. 354. The Wellington records were made by myself.

The temperature of the water in rock-pools between tides is appreciably raised on a sunny day, as the following figures show:—

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Tides.

In the Southern Ocean, south of the continental masses, the tidal wave has a clear course round the world, and from here appear to generate tides supplying the great oceans to the northward. In New Zealand the tide comes from the south, striking the south-west coast of the South Island about 12 o'clock at full and change of the moon. On the west coast it apparently meets a portion of the previous wave which has passed through Cook Strait from the east. Its course up the east coast, however, is more eventful. In two hours it has passed through Foveaux Strait from west to east, and after another hour is abreast of Taiaroa Head. Four hours after its first incidence on the New Zealand coast it has reached Lyttelton and Wellington, and after a further two hours has passed through Cook Strait in one direction and towards Napier in another. The northern branch continues round the East and North Capes and down the west coast of the North Island, reaching New Plymouth about 10 o'clock. The moiety that passes through Cook Strait from the eastward meets this northern branch in one direction south of Cape Egmont, and in another continues in a westerly course past Cape Farewell and meets the next incoming tidal wave southward of this.

The amplitude of the tide depends almost entirely on the configuration of the land. Thus at points where the tidal wave can sweep past, as in Foveaux Strait, Cook Strait, and the east coast, its range is not great. Spring tides rise at Wellington 4½ ft., at Napier 4 ft., at Taiaroa Head and Gisborne 6½ ft. Where the land converges, as in Hauraki Gulf and Tasman Bay, the effect is to bank up the water as the sea-space becomes narrower, hence such high tides as at Auckland, 12 ft., and Nelson, 12 ft. Perhaps the meeting of tides from two directions accounts for the high tides experienced on the west coast, as at New Plymouth, 11 ft., and Grey River, 10 ft.

Highest spring tides sometimes follow the full moon and sometimes the new moon. Thus at Auckland, in 1914, from January to May full moon was followed by good spring tides, but from August to December the highest tides followed the new moon.

II. Ecological, Relations.

and their distribution in the main supports this view. Thus bright-green algae are usually highest in the series, dark-green and brown algae predominate about low-tide mark, whilst red algae are most plentiful below this. The red pigment is presumed to check the harmful action of the actinic violet rays, which are proportionately stronger at a little depth than at the surface. But there are many exceptions to the order in which the classes of algae usually occur. Thus Bostrychia arbuscula and Caulacanthus spinellus, which occur highest in the intertidal belt, belong to the Rhodophyceae, while Chaetomorpha and Caulerpa are bright-green algae found amongst red algae at low-tide mark.

There appears to be a relation similar to that observed in algae between the colour of the tests of tunicates and the quality of the light received. On exposed rocks the predominant colour is some shade of brown, which may have a similar function to that of brown pigment in the Phyaeophyceae. Boltenia pachydermatina, which lives at a lower level, is of a red colour not unlike that of the Rhodophyceae. Under stones the tests are colourless, with a pink or reddish tinge (Corella), or distinctly blue (Styela caerulea).

Evaporation.

(a.) Shelled Animals.—Undoubtedly the main character by virtue of which animals are able to conserve moisture during the retirement of the tide is an external shell. The shell, by reason of its usually great strength,-is probably primarily intended for defence; but that it functions largely as a retainer of water is indicated by the fact that, with few exceptions, all animals habitually exposed to the atmosphere between tides possess shells. The shell proper is invariably composed of carbonate of lime, either in the form of arragonite or calcite, or both. It varies very much in shape, is possessed by animals widely sundered in systematic position, as molluscs and polychaet worms, and is consequently diverse in origin. One of the distinguishing features of the phylum Mollusca is the mantle, and it is this organ which secretes the shell, mainly by its edge; but additions to the thickness of the shell are made internally by the portion of the mantle behind its outer border. That there-is a direct relation between the presence of a shell and the amount of exposure to air to which the animal is subjected may be inferred from the fact that many molluscs living below low-tide mark have no shell, or only a small one covering portions of the viscera (Scutus ambiguus, nudibranchs, pleurobrancbs). Others in similar situations have only rudimentary opercula (Alcithoe, Struihiolaria).

Gasteropoda.—The gasteropod shell takes three main forms:—

(1.) It is conical, with a wide base and the apex somewhere in the median line (Cellana, Noloacmea, Siphonaria, Tugdlia, Gadinia). The gills, or, in the case of Siphonaria and Gadinia, the openings to the branchial chamber, are situated near the margin of the shell. When immersed the animal raises its shell off the rock and allows the water to circulate underneath, where it serves the purpose of respiration. These limpet-like animals are mainly vegetable feeders, and do not move about the rocks to any extent. When the tide retires, the shell is appressed to the rock-surface sufficiently tightly to prevent the enclosed water from escaping, and thus the animal remains in a bath of salt water until the return of the tide.

(2.) The shell is ear-shaped—that is, it has a broad elliptic base several times longer than the height, and the apex is spiral and marginal. There is a row of branchial apertures along a lateral carina (Haliotis). The provision for conserving moisture is here obviously imperfect, and these animals are therefore rarely found above low-tide mark.

rocka. They are air-breathers, and the pulmonary orifice which opens in the posterior portion of the under-surface of the body is closed while the animals are under water. The Onchidellae may be contrasted with nudi-branchs and aplysoids, which live at or below low-tide mark and have the branchiae but little protected and on the upper surface of the body.

(e.) Algae.—In algae the main protection against atmospheric conditions is dense thick-walled tissue on the outside of the thallus. Thus in Bostrychia arbuscula the outer layer is composed of thick-walled polygonal cells containing olive granules. In Cystophora dumosa there are one or more rows of oblong cells with their long axes at right angles to the periphery, and with moderately thick cell-walls. Within this layer is large-celled parenchyma. Lessonia variegata, has on each side of the thalluslamina three or four rows of minute densely aggregated cells with clear walls and olive-brown granules. Within these is a transparent tissue of large cells, and in the centre a band of mechanical tissue. A dense outer cortex followed by large-celled medullary tissue is also found in Durvillea antarctica, Carpophyllum maschalocarpum, and Xiphophora chondrophylla, descriptions of which are given under the heading of the associations of which they are the dominant members. (See figs. 1–3, 5, 6.)

(f.) Water-reservoirs in Algae.—Two species of brown algae living well up in the intertidal belt have a hollow thallus filled with a watery substance. In Hormosira Banksii the internodes are swollen and filled with water. In Splachnidium ruqosum the central space is continuous and contains a watery jelly. In Adenocystis utricularis and Colpomenia sinuosus, which live nearer low-tide mark, the whole thallus is saccate and filled with water.

(g.) Covering of Slime or Mucilage.—Many algae have a covering of slime on the outside. Splachnidium, rugosum and Codium adhaerens are exceedingly slimy. Ulva and Porphyra possess a thin coat, which on drying is slightly sticky to the touch. A covering of slime is frequent in many marine animals.

Sea-water.

(a.) Buoyancy.—As with land-plants, algae are so constructed as to display their vegetative structure as much as possible to the surrounding medium and to the light. On account of the movement of the water, rigid tissue is inadmissible in the littoral belt except for very-low-growing forms (Corallina, Meldbesia). Devices for keeping algae upright in the water are of the nature of buoys, and may be special air-vesicles, expansions of the thalli, or large air-cells. The air-vesicles vary in shape and position. In Cysptophora, Marginaria, and Carpophyllum they are globose and terminate short branches. In Macrocyslis pyrifera it is the stalks of the leaf-like fronds that are enlarged into elongate pyriform vesicles. Large air-cells are best seen in Durvillea antarctica, where they are polygonal and columnar, stretching across the frond at right angles to the plane of the lamina.

(b.) Acidity.—Erosion in molluscan shells has been ascribed to acidity in the water by nearly all authors who have written on the subject (Lewis, Bost. Soc. Proc., vol. 6, p. 149; Tryon, Struct. Syst. Conch., vol. 1, p. 19, 1882; Cooke, Cambr. Nat. Hist., vol. 3, p. 276, 1895). The observations here recorded appear to support this view. Erosion almost invariably begins on the apex of gasteropods or umbones of pelecypod shells—that is, on those parts which are longest exposed to the action of the air or water. To strengthen the parts of the shell thus worn thin

Edaphic Factors.

tide-marks, frequenting the under-side of stones, where it remains in wet mud or shallow pools while the tide is out. Its median fins, both dorsal and anal, are long, with rays of even height. The tips of all the rays except those at the posterior ends are swollen. It is suggested that these swellings are special organs, possibly sensitive, for pushing against the rocks above and below, and are thus an adaptation to the fish's habit of wriggling its way along under stones. (Plate 42, fig. 6.)

(d.) Rock.-borers.—Many animals burrow into the softer kinds of rocks, and probably have organs especially adapted for this purpose, though their methods are not well understood. Pholadidea spathulata, Barnea similis, and Lithophaga truncata are found commonly boring into Tertiary sandstones in Rangitoto Channel. The entrance is in every case smaller than the main portion of the burrow, so that the animal is a prisoner. The method of enlarging the burrow has been observed in the exotic genus Pholas: the animal rasps the rock with its shell. Lithophaga has an acid-secreting gland, presumed to be the source of a solvent for dissolving limestone rock (Calman, Rep. Comm. Inst. Civil Eng., 1920, p. 73). A small crustacean, Sphaeroma quoyana, is also very abundant, boring into the same rock as the bivalves mentioned.

Sand.

The main character of a sandy beach, so far as the life found there is concerned, is its movement, caused by wave-action. Only animals capable of burrowing quickly can exist in the surf-swept shore. Hedley has pointed out that the shells of sand-dwellers are solid, smooth, and tapering, citing Donax deltoides of the New South Wales coast as an instance. The truth of this statement is borne out by the character of two species of Amphidesma found in New Zealand, both of them being inhabitants of the ocean-beach. The foot is large and powerful, and the shell tapers gradually towards the anterior end, thus offering little resistance to the sand. The siphons are long—indeed, those of Amphidesma ventricosum can be extended to 15 cm. or 20 cm., so that the animal may remain with its shell at this depth below the surface and so minimize the risk of being thrown up by the surf. But not all sand-dwelling pelecypods have smooth tapering shells. On the ocean-beach near Tauranga, where Amphidesma subtriangulata exists in countless thousands, there also occurs associated with it, in numbers equally great, Antigona spissa, a small species with ventricose shell roughened by concentric ribs.

Brittle-stars inhabiting the sand-beach are furnished with extremely long, thin arms. Amphiura aster at Timaru, and the same or an allied species in Rangitoto Channel, remain with their bodies buried in the sand at a depth of 10 cm., but the tips of the arms project above the surface, and attend to the wants of the animal below. Polychaets are rapid burrowers, as any one who endeavours to dig them out soon discovers. Gasteropods living in sandy beaches are in the habit of ploughing their way along just below the surface. The foot is frequently large, with its lobes reflected partly over the shell (Ancilla, Natica). In Struthiolaria it is similarly very broad.

The pelecypod Pinna zelandica in Rangitoto Channel is found buried upright in sand. Passing downwards between the valves near the anterior end is a large byssus composed of numerous spreading threads, to the extreme end of each of which is fastened a grain of sand.

Movement of Water.

Perhaps the most potent of factors in the littoral belt with which the inhabitants have to contend is the movement of water. Tidal currents are the cause of the more gentle and steady movements along a coast; in an estuary, however, they may be very strong and exert a powerful action on the flats, masses of Zostera being frequently torn away and carried out to sea. The most violent action of the sea is caused by waves which reach their maximum strength during storms. The power of the surf may be gauged by the damage done by heavy seas to breakwaters and other harbour constructions. The most characteristic modifications of plants and animals inhabiting the intertidal belt appear to be adaptations caused by the motion of water. This is shown by their shape, strength, pliancy, and by their devices for holding on to objects. Hedley has noted the tent-like form and the strength of molluscan shells on the rocky coast of New South Wales (1915, p. 58). Some adaptations to water-movement observed in animals and plants in the littoral belt in New Zealand will here be described.

(1.) Tent-like Form.—To offer least resistance to the surf the animal must be attached to the rock by a broad base, have sloping sides and a fairly low apex. Hence results the tent-like form so prevalent on rocky coasts, and independently acquired by members of several classes of animals.

(a.) Gasteropoda.—A conical shell with a more or less oval base characterizes the members of the Patellidae, Acmeadae, Siphonariidae, and the genera Tugalia and Gadinia. There is an apical foramen in Fissuridea and Puncturella, and an anterior marginal slit in Emarginula.

(b.) Amphineura.—In proportion to basal area members of this class offer less resistance to the surf than do the tent-like gasteropods. The

of the water. The thalli of Durvillea antarctica on exposed coasts assume the form of long narrow segments of nearly even width throughout. In more sheltered situations the thallus is broadly and irregularly palmate. Xiphophora chondrophylla, perhaps the most abundant species of brown algae occurring at low-tide-mark, has the thallus-segments uniformly narrow. In the size of the “leaves” of Carpophyllum an interesting comparison may be made between C. maschalocarpum, which grows in fairly exposed placed and has small thick leaves, and C. phyllanthus, which affects harbours and sheltered inlets and is a very luxuriant form with large thin leaves. Macrocystis pyrifera, which possesses the largest and most easily torn leaves of the brown algae, occurs chiefly inside harbours, especially in tidal streams, and in deep water outside the break of the surf.

The ribbon-like leaves of Zostera and Ruppia need only be mentioned here. These plants live in stations subject to tidal currents, but not to much wave-action. The action of waves is irregular and discontinuous, whereas that of currents is regular and constant, and this is reflected in the difference between branched and unbranched stems. Mr. W. A. Scarfe informs me that the ribbon-like form of Durvillea antarctica only occurs in places where current is added to wave-action.

(5.) Hooked Claws.—Certain crustacea living on algae exposed to the surf are provided with sharp claws, which enable them to retain their positions while the seaweed is being buffeted about by the waves. Their use is in every respect similar to that of the hooks possessed by various crustacea living on fishes and cetaceans. Species of Idotea occur on various algae in the surf belt; their legs all terminate in hooked claws. Amphoroidea falcifer is found on Durvillea antarctica, and by its depressed form and strong hooks is admirably adapted to its station.

Organic Environment.

(1.) Armour.—Perhaps the most universal of devices for protecting sedentary marine animals against enemies is the possession of shelly armour. This is probably the primary use of shell and operculum. But, as I have pointed out in a previous paragraph, these are also of service in the littoral belt for conserving moisture. Hermit-crabs, which have the hinder portion of the body quite unprotected, make use of empty gasteropod shells.

(2.) Weapons.—Closely associated with armour are weapons of defence and attack. The chelae of crabs may be first mentioned. Powerful jaws are possessed by many polychaet worms; gasteropods employ their radulae for boring through the shells of their prey. The spines of echinoids and the stinging-cells of sea-anemones are effective weapons.

(3.) Distasteful properties are possessed by many animals and plants. The common sponges are quite unpalatable, owing to the presence of siliceous spicules. Their evil smell also probably helps to keep off would-be enemies, whilst the bright colour of many of the species perhaps serves as a warning to other animals. The calcareous deposits in Corallina, Amphiroa, and Melobesia render them safe from the depredations of herbivorous animals (fig. 4).

(4.) Assimilative Colouring.—Instances of patterns of colouring resembling the surroundings, be it rock or algae, among which the animals live are frequent in the littoral belt, and are presumed to be mainly for protective purposes. Fishes of the families Blennidae and Gobiesocidae are of various shades of black, grey, and pink with a mottled pattern. Nudibranchs and

tectibranchs are sometimes of mottled greys like Pleurobranchus novae-zealandiae, or reddish-brown with darker blotches as in P. ornatus—that is, they resemble the surroundings generally. Others are so coloured as to resemble only the algae or sponge on which they are found. Thus Ctenodoris flabellifera is yellow, and Rostanga rubicunda bright scarlet, and these are found on sponges similarly coloured. The free sea-anemone Phlyctenactis retifera is coloured olive-brown like Cystophora dumosa, on which it lives. Crustacea are green (Paridotea ungulata), brown (Amphoroidea falcifer, Idotea elongata), or red (Paridotea peronii, Dynamenella huttoni), according to the colour of the algae on which they are found. The suckerfish (Trachelochismus guttulatus), living in the brown-algae formation in Wellington Harbour, is olive-brown. Finally, some shrimps are colourless.

(5.) Masking.—Deliberate masking by carrying pieces of shell, seaweed, or stones is practised by the sea-urchin Evechinus chloroticus. Certain crabs (Paramithrax) place on their carapaces pieces of seaweed, which become fixed and grow, forming little gardens, completely masking the crabs, which, knowing the protection afforded, usually keep in places where seaweed is growing. I once watched one of these crabs walking across the sandy bottom of a pool. On coming into my shadow it suddenly stopped, paused for a moment, then hurried back to the seaweed-covered rocks.

Many animals have their shells or tests (Tunicata) masked by algae, Vermilia, barnacles, sponges, and other forms of life. These probably merely settle uninvited on the vacant space. Nevertheless, they must subserve to some extent the purpose of concealment. Mud- and sand-dwelling pelecypods (Pinna, Antigona, Amphidesma) frequently have the posterior projecting end of their shells covered with various forms of marine growth. Too much growth on the shells sometimes results in the destruction of both the mollusc and the life it supports. In the Bay of Plenty, after a storm, it is a common thing to find Venericardia purpurata with the sponge Chalina 30 cm. or more in length washed up on the beach.

(6.) Animals and Plants.—Some animals appear to be specially modified for attachment to algae. When Siphonaria australis lives within the base of the holdfast of Durvillea antarctica it is usually found on the roof of the chamber, occupying hollows in the algal tissue. Here the foot of the mollusc fills up the hollow and projects beyond the shell-margin, the shell itself becomes depressed sometimes to the point of becoming quite flat, and the margin is slightly recurved.

Notoacmea scapha is found in Tauranga Harbour living on the leaves of Zostera nana. Its narrow shell seems a special adaptation to this station. The hooks of the isopods Idotea and Amphoroidea for holding on to algae have already been mentioned.

III. Biotic Communities.

Animals and plants inhabiting the littoral belt are found to group themselves in communities, many of which are sharply separated from one another. These I refer to as “biotic communities” because, whatever the limits assigned to them, whether from a consideration of the species they include or of the habitats, it is found that in every case both plants and animals form integral parts. The term “growth-form” has been defined as including all those species which agree in their external form, anatomical structure, and behaviour. A biotic community consists of a definite set of growth-forms in relation to a definite habitat. The growth-forms occur

in definite relation to each other as well as to the inorganic surroundings. In the environment there are many factors involved in climate and substratum, and the different combinations of these give many different habitats. Because, therefore, of differences in the external conditions, and of the dominance of certain growth-forms and different relationships of others, there arise many distinct communities of plants and animals.

Formations.

The reporters to the Commission of Phytogeographical Nomenclature (Brussels, 1905) recommended that a plant-formation should be defined as composing associations of species which differ in their floristic composition but are in agreement, firstly, with the conditions of the habitat, and, secondly, as regards their growth-forms. Were this definition applied strictly every community having a different growth-form as its dominant member would be considered a different formation. In a New Zealand forest there are several different growth-forms in trees, and we might accordingly have many forest formations, such as those where Agathis, Beilschmiedia, or Nothofagus are dominant. In the littoral belt the multiplicity of formations so defined would be very great. Because of the diverse origin of the plants and animals inhabiting it, there are many growth-forms that are dominant in certain areas. Now, different growth-forms often require the same amount of water and the same quantity and kind of food supplied to them daily—that is, they bear similar relations to their surroundings. To use an expression of Shelford's, they may be said to be ecologically equivalent in respect to a given factor. These physiologically similar growth-forms, hereafter referred to as ecological groups, appear to be the important units concerned in the differentiation of formations. I would therefore define a formation as a biotic community having its ecological groups in definite combination and in relation to a definite environment. Examples of growth-forms ecologically equivalent, and therefore belonging to the same ecological group, will show the importance of the physiological requirements of the organism being taken into account, and the small value that can be placed on external features, which, however, may be so different as to justify separation into distinct growth-forms. A sessile cirripede (Elminius), a pelecypod (Mytilus), and a polychaet worm (Vermilia) may grow side by side, existing under precisely the same conditions as regards supply of moisture and exposure to the surf, and each will filter water through its branchiae or other organs for the same period each day, and will digest similar minute organisms. Each also can efficiently protect itself against the drying effects of exposure while left uncovered by the tide. These animals, which are widely sundered systematically, have quite different growth-forms, but belong to the same ecological group. Similarly, the algae Hormosira Banksii and Scytothamnus australis are ecologically equivalent as regards ability to endure exposure to the atmosphere. Yet each is differently constructed for this purpose: the one has an internal water-reservoir, the other a protective covering of tissue that reduces transpiration; and they thus belong to different growth-forms. It is the ecological groups that I have utilized to define the formations between tide-marks. For instance, the shelled-animals formation always has for its dominant member an animal capable of conserving moisture in its shell while exposed to the atmosphere. Such an animal may be a cirripede, a pelecypod, a gasteropod, or a polycheat worm.

There are certain constant spatial relationships among the growth-forms in each formation. In the microlithic substrata two or three main tiers of

life are recognized—namely, the subsurface, or burrowing, organisms; the surface, or crawling, animals; and, when a plant is dominant, the supra-edaphic plant-form and its dependent life. On rocks in the shelled-animals formation there is usually only a single stratum of life with a fixed or sedentary animal dominant. If the rocks are broken there may be an assemblage of animals underneath the stones, usually differing markedly from those above, and forming a subformation dependent on the damp conditions. The intertidal formation possessing the greatest variety of growth-forms is that in which large algae are dominant. Associated with these are animals and plants on the rock-surface, in crevices, and under stones, on the thalli of the algae, and, when Durvillea is present, peculiar assemblages of animals inhabitating cavities in the discoidal holdfasts. Each formation may therefore be said to have a definite structure depending on the nature of the substratum and the dominant growth-form.

As some formations appear to be more closely related than others, it may be convenient to group them into classes. These I call “series,” and they are characterized by the physiological requirements of the dominant ecological groups. Formations may likewise be divided into subformations according to the dominant growth-forms. Thus the shelled-animals formation includes four subformations—pelecypod, sessile cirripede, tubicolous polychaet, and gasteropod. Each of these comprises one or more associations which are communities of definite floristic and faunistic composition. Differences in the principal species might be utilized to define subassociations, but I have not treated the subject in such detail in the present paper.

Classification of Littoral Biotic Communities.

An animal-and-plant formation has been defined as a biotic community with its principal ecological groups in definite combination and in definite relation to the habitat. The community is thus looked at from the point of view of its growth-forms and environment, and one formation is distinguished from another by a difference in the dominant ecological group of growth-forms. The dominant growth-forms in the littoral formations are always fixed animals and plants deriving nutriment from the sea-water, including its microscopic life, or else sedentary animals living on small benthic organisms. Carnivorous and herbivorous animals which feed on other large animals or plants can never be dominant forms in any permanent association. The number of tiers or strata in a formation depends primarily on the substratum, which may be impenetrable to plants and animals alike, as rock, or it may be easily burrowed into by animals or penetrated by the roots of plants, as sand and mud. This difference is fundamental, as, though formations are interchangeable on a microlithic substratum on the one hand or on rock on the other, according to supply of moisture, the formations of mud and sand can never invade a rocky coast, nor can the opposite change take place. Littoral formations, therefore, can be classed under two main heads—(1) Formations on rock with the dominant form varying from algae to shelled animals according to the diminishing supply of water. Animals and plants firmy fixed to the rock-surface are the main features of the rock-formations. (2) Formations on sand and mud, varying from animal to plant according to height above low tide—that is, in the reverse order to that observed in rock-formations (but Zostera is an exception to this rule). Burrowing animals and rooted plants are characteristic of this group.

The following table gives a classification of formations in the littoral belt. Definitions of each formation and descriptions of typical associations are given in the next section.

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Large-brown-algae Formation.

always isolateral. Two or more distinct associations are to be recognized: Durvillea antarctica is dominant in an association characteristic of the south, whilst Carpophyllum maschalocarpum is the principal species in an association extending throughout New Zealand. Where there is a level rocky bottom above the Durvillea association a Xiphophora association may be developed.

The large-brown-algae formation appears to be best represented in temperate seas. In Tasmania and the southern coasts of Australia Durvillea potatorum is dominant in an association comparable with that of Durvillea antarctica in New Zealand. Outside New Zealand, D. antarctica is recorded from Kerguelen, South Georgia, and the Falkland Islands. An association described by Hedley from New South Wales (1915, p. 59) has Eclonia radiata and Sargassum tristichum as leading, species, and is externally similar to the association in Hauraki Gulf, where Eclonia Richardsoni and Carpophyllum maschalocarpum take their place. In the North Atlantic these are represented by Laminaria digitata and Fucus vesiculosus (Cotton, Transeau). In warmer waters the principal algae are smaller and the species fewer. In Queensland species of Sargassum are dominant (Johnston, 1917, p. 55); in Tahiti the outside reef supports a low growth of Sargassum and Turbinaria.

DurvilleaAssociation.

This association is characterized by the presence of the large kelp Durvillea antarctica. This alga stands out above the others like a lofty tree in a forest, forming a tier of vegetation by itself. Below is a growth of Marginaria, Lessonia, and other algae equivalent in size and appearance to those dominant in the Carpophyllum association, where Durvillea is absent. Durvillea is thus like an extra form imposed on an association of smaller algae, but it may become so dense as to displace many of the smaller kinds. Durvillea always grows in exposed places, and appears to be confined to the surf belt, not extending into deep water. It assumes two forms, one with broad thalli, the other with long narrow segments, this latter form occurring in places exposed to tidal currents. A characteristic fauna is found in cavities hollowed out of the large holdfasts of Durvillea.

Durvillea has a tough outer layer of twenty or thirty rows of oblong cells placed with their longer axes at right angles to the surface, as in palisade tissue. These cells have thick walls, and are filled with brown granules, which are most dense along the outer edge. Beneath this follows a layer, twice as thick as the palisade layer, of interwoven branched nucleated septate threads, similar in appearance to fungal hyphae. Some of this tissue consists of a mixture of filiform and isodiametric cells. The central tissue is composed of a single layer of very large columnar polygonal cells stretching across at right angles to the lamina. (Fig. 3.)

The Durvillea association is well developed in the south of New Zealand, extending as far north as Cook Strait on the east and to north of Manukau Heads (Te Henga) on the west. It occurs also at the Chatham Islands. The species is recorded elsewhere in the New Zealand area from the Snares, Auckland, and Campbell Islands.

Shag Point.—Along the outer margin of rocks about low-water mark there occurs a regular marine forest of the large kelp Durvillea antarctica. This species forms the most conspicuous feature of the tidal rocks when the water is low, but it merely dominates a much denser growth of other large brown algae. The Durvillea plants are attached to the rocks by broad disc-like holdfasts, usually fixed in elevated positions. From the holdfast

along the upper level of the association. This alga grows so thickly that its wide thalli when lying on the rocks cover up entirely all the other vegetation. The holdfasts here are small compared to those found farther south, and the life they shelter is not so varied. Which species first bore into them I am unable to say, but Siphonaria australis is an early visitor. Other species found in the holdfast-cavities are Onithochiton neglectus, Plaxiphora egregia, Sypharochiton sinclairi, and Sphaeroma.

Along the upper margin of the Durvillea association there is a belt of Xiphophora chondrophylla. Lower down larger brown algae occur: they are principally Marginaria Boryana, Lessonia variegata, Carpophyllum maschalocarpum, and Cystophora dumosa. Beneath these the rock-surface is completely covered with corallines—Amphiroa, Corallina, Melobesia—and a number of small red and brown algae, such as Pterocladia lucida, Zonaria Turneriana, Glossophora Harveyi, and Stypocaulon paniculatum.

Animals found on the rocks in this association include Patelloidea stella corticata (abundant and always covered with Melobesia), Haliotis iris, H. australis, Siphonaria zealandica, Sypharochiton sinclairi, Patiriella regularis, and a few tunicates. On the fronds of Lessonia occur Cantharidus opalus and C. purpuratus. (Plate 43, fig. 2.)

Te Henga.—This locality, north of Manukau Heads, is near the northern limit of Durvillea antarctica. The kelp here grows in a belt on the rocks, extending to about 1 m. above low-tide mark, and exposed to the full fury of the westerly seas. Where it is fairly dense its long thalli hang down and entirely hide the rock-face from view. The rock is covered with Melobesia, while scattered over it fairly thickly are some brown and red algae.

There are few molluscs on the rocks. Sypharochiton sinclairi is common; Plaxiphora obtecta, with clean non-eroded shells, is found here and there; and P. caelata also occurs. A single small specimen of P. biramosa was found. A large starfish, Stichaster australis, is extremely common and very conspicuous: it varies in colour from red to purple. Underneath the holdfasts of Durvillea is Venerupis reflexa.

Carpophyllum Association.

This association is found from the North Cape to Stewart Island. Carpophyllum maschalocarpum, the dominant plant, has small elliptic thallus-segments, 2–3 cm. long and½–1 cm. wide. There is an outer row of cells about five times as long as wide, with the long axes at right angles to the surface, and brown granules at the inner end. Following this is a dense tissue, thicker near the middle of the thallus-segment than near the margins, of cubical cells with thick walls and containing brown granules. The central tissue is composed of quite large cells; those next the tough cortex just described are polygonal, those in the centre elongated and forming denser tissue. (Fig. 6.)

Rangitoto.—At the Beacon Reef, on the north-west side of Rangitoto, a large-brown-algae formation is well developed. On rocks exposed only at spring tides and extending below low-tide mark for a little distance there is a dense growth, 20–30 cm. tall, composed mainly of four species of brown algae. Carpophyllum maschalocarpum and C. plumosum are perhaps dominant over most of the area; Xiphophora chondrophylla is most abundant along the upper margin, and Eclonia Richardsonia in the lower portion. Sargassum Sinclairii and Cystophora dumosa are also fairly common. On the brown algae are found plentifully Trochus viridis, T. tiaratus, and Cantharidus dilatatus, all herbivorous gasteropods having

Small-emerging-algae Formation.

Corallina are not so obvious. The deposit of carbonate of lime may be of some use in this respect, but of this there appears to be no evidence.

Four subformations based on the dominant growth-form may be distinguished—namely, coralline algae, small brown algae, ulvoid algae, and small olive-red algae. Corallina is dominant on exposed rocks above the brown-algae formation, Hormosira on level rocks in harbours; more usual, however, Corallina and Hormosira are fairly well mixed. Porphyra or Uiva form associations in various localities, whilst higher up on the rocks Bostrychia in the south and Caulacanthus in the north form well-defined associations.

Corallina associations appear to be found in all seas. They have been described from such widely-sundered localities as Ireland (Cotton, p. 39), New South Wales (Hedley, p. 58), and Hawaii (MacCaughey). Porphyra and Ulva associations are equally widely distributed. An association of Hormosira Banksii is extensively developed at Long Reef, New South Wales, and differs from similar associations in New Zealand only in the associated species of animals.

Coralline-algae Subformotion.

The association in which Corallina is dominant is found throughout New Zealand on exposed coasts above the large-brown-algae formation, and in rock-pools between tide-marks. It forms a low growth of little tufts, which collect quantities of sediment, especially in sheltered situations. The most common association of algae in the mid-tide belt in New Zealand is that of Corallina and Hormosira. Corallina appears to require more water than Hormosira, being always found in wetter situations. Also, while Corallina is found exposed to the strongest surf, Hormosira is never found in such places. The Corallina-Hormosira association is best developed in harbours. Both plants are tolerant of a certain admixture of fresh water, and of mud with the sea-water. Associated with these algae are always a number of shelled animals—molluscs, worms, sessile barnacles.

Corallina Association.

Tauranga. — Immediately above the brown - algae formation on the North Rocks, Mount Maunganui, there is a belt more or less covered with Corallina officinalis and other small algae. There is also a good deal of Elminius modestus, and in crevices Vermilia carinifera. On the rocks are many molluscs—Cellana radians, Sypharochiton pellisserpentis, Lepsiella scobma; also the starfish Patiriella regularis.

Auckland Harbour.—In pools on the reef stretching towards Kauri Point the rocky bottom is covered with Corallina officinalis mixed with Colpomenia sinuosa and other small algae. There are a few sponges, while Turbo smaragdus and Cerithidea subcarinata are abundant. Small examples of Amaurochiton glaucus occur on the shells of Turbo, whilst Dardanula olivacea swarm among the Corallina.

Corallina-HormosiraAssociation.

Takapuna.—Here are extensive areas of volcanic rocks covered with a Corallina-Hormosira association fairly uniform in composition. Corallina officinalis affects wetter situations than Hormosira Banksii, so that in shallow pools one finds that Corallina covers the bottom while Hormosira occurs as a fringe round the edge, and on rough surfaces Hormosira is found

on the projections and in the hollows. In the lower portion of the association occur Scytothamnus australis, Colpomenia sinuosa, and, in shady places, Codium adhaerens. Cerithidea subcarinata is abundant on the Corallina, especially in rock-pools. The principal mollusc, however, is Turbo smaragdus, which occurs plentifully on algae throughout the whole association. It has attached to its shell small Elminius modestus and Crepidula crepidula. Other molluscs are Hdustrum haustrum, Neothais sucdncta, Cominella maculosa, Lepsiella scobina, and Sypharochiton pellisserpentis. (Plate 44, fig. 1.)

Bay of Islands.—At Long Beach this association is developed on rocks above the brown - algae formation and below the Ostrea association. Hormosira Banksii is plentiful, especially in crevices and small pools. Mixed with it is Colpomenia sinuosa, and a few plants of Xiphophora chondrophylla. Corallina officinalis covers the bottom of rock-pools. On rocks round the edges of crevices containing water is Caulacanthus spinelhis. The rock-surface is almost completely covered with a veneer of Elminius modestus. Common everywhere, chiefly in crevices during exposure, by the tide, are Turbo smaragdus (on algae), Sypharochiton, pellisserpentis with much-eroded valves, Vermilia carinifera (sometimes forming patches), Nerita melanotragus, Lepsiella scobina with eroded shells carrying small Elminius, Cellana radians, Elminius plicatus, and a few Anomia walteri with thick eroded shells bearing Spirorbis.

Shag Poin.—Between tide-marks at Shag Point are some fairly wide stretches of nearly level rocks. Just within the outer edge with its formation of brown algae there are regular meadows of small algae 4 cm. to 5 cm. tall. Generally the rocks are completely covered, and the association differs according to exposure. Over most of the area the dominant species are Corallina officinalis and Hormosira Banksii; but many other species occur, all, however, of low growth. Standing out among the close growth are Colpomenia sinuosa and Adenocystis utricularis, both possessing hollow thalli, generally full of water. In crevices are found larger algae, such as Cystophora dumosa.

Most conspicuous among the mollusca in this association is Turbo smaragdus, which occurs abundantly throughout, and supports on its shell the crustaceous brown algae Leathesia. A few Turbo granosus may be seen; also present are Cantharidus tenebrosus and Monodonta aethiops. Occurring in the algae are the small pelecypods Lasaea miliaris and Verticipronus mytilus, and the amphipod Hyale hirtipalma; also the worms Nereis vaucaurica, Onuphis tubicola, and Lumbriconereis spherocephala. Where there are bare spaces on the rocks Patelloidea stella corticata covered with Meldbesia, Cellana radians, and Sypharochiton pellisserpentis will be found.

Towards low-water mark Hormosira is not found, and Corallina officinalis is no longer dominant. Instead is a thick low growth of Stypocaulon, Ballia, Nitophyllum, numerous corallines, red weeds and Chaetomorpha. Mollusca occur on the rock-surface under the algae. In such situations are Cellana radians, Plaxiphora caelata, Sypharochiton sinclairi, and Acanthochiton zealandicus. (Plate 44, fig. 2.)

Small-brown-algae Subformation.

Hormosira Banksii, when dominant, usually forms a nearly pure association, as far as algae are concerned, on level rocks between tides in harbours. Such an association is well developed at Waitangi, Chatham Island, and near Purau, in Lyttelton Harbour. Hormosira can endure long exposure

to the atmosphere, being enabled to do so by a large quantity of water contained in the hollow and distended internodes. The influence of fresh or turbid water seems not in the least harmful to this alga. There is a cortex of four or five rows of rectangular cells arranged like palisade tissue and filled with brown granules. Beneath this are the large polygonal cells of the medulla, the outer ones of which have brown granules. Inside this to the central water-chamber are straight septate filaments.

Chatham Island.—The sea-water in Waitangi Bay is very much discoloured by the peaty water discharged by the Waitangi River. The rocks are soft brown sandstones shelving between tide-marks. Above the large-brown-algae formation there is a considerable area covered with Hormosira Banksii. This alga grows very thickly, completely covering the rocks. Underneath there is little life, only Monodonta coracina and Sypharochiton pellisserpentis being seen; but on the rock where Hormosira is more open there are numerous gasteropods. Cerithidea subcarinata is abundant; also common are Cominetta maculosa, Haustrum haustrum, Monodonta aeihiops, and (especially near the upper margin of the belt) Melaraphe unifasciata, M. cincta, Siphonaria zealandica, and Cellana strigilis. (Plate 45, fig. 1.)

Ulvoid-algae Subformation.

Two associations are here included: one consists of Porphyra columbina, on rocks about half-tide mark; the other of Ulva rigida, often in situations subject to the influence of fresh water. Both these species, though having broad, delicate thalli, are able to remain for a considerable period exposed to the atmosphere. Porphyra under these circumstances shows signs of wilting. On drying, both species have a glistening appearance, due to a thin coating of mucilaginous matter, which probably assists in preventing excessive transpiration.

Ulva Association.

Rangitoto.—On the north coast of Rangitoto is a small pool separated from the sea by a shingle-bank. Into this the sea must penetrate, for it contains brackish water and an association of marine organisms. There is a thick growth of Ulva rigida. The animals include Sypharochiton pellisserpentis, Monodonta aeihiops, and some sea-anemones, all of which are abundant. Less common are Acanihochiton zealandicus, Lepsiella scobina, Cerithidea subcarinata, and Patiriella regularis. The Acanihochiton and Patiriella are whitish, and all the other shells are more or less eroded.

Porphyra Association.

Cook Strait.—At Lyall Bay there is a well-marked association of Porphyra columbina, which occurs in patches, especially covering rocky platforms not far above the level of half-tide. In many places it grows so thickly that it entirely hides from view areas of rock 2 m. or 3 m. across. Exposed to the air, the thallus lies flat on the rocks. When, dried it has a glistening appearance, due to a coating of mucilage. The tips are frayed, as if suffering from wilting during too severe drying conditions. The colour is very varied, owing to different degrees of exposure. The base, which gets most protection, is dark green or brownish-green; exposed parts are reddish or pale green. Associated algae are a few plants of Ulva and some small filamentous red kinds.

The animals occurring with Porphyra are those of the Chamaesipho association, which occupies most of the mid-tide belt hereabouts. They

include Chamaesipho columna, Elminius plicatus, Cellana ornata, C. denticutata, Siphonaria obliquata, S. zealandica, Risellopsis varia, and Melaraphe cincta; also Sypharochiton pellisserpentis in crevices, and Melaraphe unifasciata in the upper portion of the association.

Small-olive-red-algae Subformation.

Two associations of small close-growing algae are included. The Bostrychia association occurs high up in the intertidal belt, where it occupies patches of various sizes on the rocks. It always harbours small pelecypods and gasteropods. Bostrychia arbuscula has an outside layer of tissue with thick-walled polygonal cells. Under drying conditions of the atmosphere it shows signs of wilting, the tips of the filiform thallus-segments curling up. This association is confined to the south of New Zealand. I have not observed it farther north than Shag Point, Otago.

Caulacanthus spinellus is more widely distributed, and is the northern representative of the small-olive-red-algae subformation. It occupies patches of rock above the belt of Ostrea cucullata, usually affecting shady places. It is of low, dense growth, and harbours small pelecypods, worms, and other animals.

Bostrychia, Association.

Stewart Island.—The upper belt of intertidal rocks at Golden Bay is characterized by an association in which Bostrychia arbuscula takes the chief part. This species covers patches of the rock to a height of about 20 mm., growing in little tufts. The belt it occupies would be exposed to the atmosphere for more than twelve hours daily. The tips of the thalli are filiform, and curl up in the sunshine and wind. At the base of this alga is found abundantly the small pelecypod Lasaea miliaris and small amphipods. Also characteristic of this association are Melaraphe cincta, some small Elminius modestus, Risellopsis varia, Notoacmea parviconoidea, and Modiolus pulex. Under stones one finds Atalacmea unguis- almae, Leuconopsis obsoleta, and small Monodonta coracina.

St. Clair.—On rocks near high-water mark there is a well-marked belt composed of a close growth, 1–2 cm. tall, of Bostrychia arbuscula. The plant alters very little in appearance when left by the tide, though it may be exposed for eighteen hours a day. Bostrychia arbuscula forms large patches, it being the only alga found here in any quantity near the top of the tidal belt. Its base collects a little sand, and here is found Lasaea miliaris, and small examples of Modiolus pulex and Elmimus modestus. Crawling over the Bostrychia are large numbers of young Melaraphe cincta, with black, shining, depressed shells up to 5 mm. long. Other molluscs occurring in this association are the young of Lepsiella scobina and Siphonaria zealandica.

Shag Point.—Here this association is developed in patches above half-tide mark. There is a fairly dense growth of Bostrychia arbuscula, 1–1·5 cm. tall. The bases of the thalli are flat, give off branches on each side, and at the ends clusters of filaments 0–1 mm. in diameter. On the rock-surfaco are small specimens of Chamaesipho columna and Modiolus pulex. The alga grows on these as well as on the rock. Among the bases of Bostrychia are crowds of Lasaea miliaris, 2–3 mm. in length. These shells contain young up to 0–6 mm. long. Young shells of Melaraphe cincta up to 6 mm. are abundant, all shells from 2 mm. to 3 mm. and longer having the spire eroded. The young of Risellopsis varia are not common, but occur up

Cobiaceous-coated-animals Fobmation.

mark near the outer extremity of this reef. Two such communities are very conspicuous: one is that of Vermilia carinifera, quite the most remarkable of its kind I have seen; the other is an association in which the tunicate Cynthia is the dominant form. This species occupies a belt of rocks extending from low-water mark at spring tides to nearly 1 m. in vertical height above. It occurs usually in clusters, some twenty or thirty being united, and attached to the rock or to an adjoining cluster at five or six places only. The depth of the covering thus formed is about 5 cm. (Plate 42, fig. 3.) The tunicate does not completely, cover the rock, but occurs in patches 10 cm. to 20 cm. in diameter. The angles of the rocks are preferred, and small irregular rocks are quite covered, but the smooth rocks are usually more or less bare. The fact that the individuals in a cluster can be separated, though with difficulty, shows that the mode of forming clusters is simply by the young settling on the outside of the tests of older individuals and growing there. Many young can be found in such positions. The tests, where touching, are joined together very firmly by their stringy and glutinous exteriors, and thus compact clusters are formed. Another larger species of tunicate occurs singly along the lower portion of the association.

Frequently embedded in the masses of Cynthia occur little colonies of Musculus impactus, each spinning round its shell a nest resembling a cocoon. Growing on the tunicate clusters are many plants of a small brown algae which swarms with Rissoina olivacea. Many gasteropods are found on and among the clusters; most common are Euthria vittata, Turbo smaragdus, Murex octogonus, and Cerithidea subcarinata, which swarms over rocks, algae, and tunicates alike. The half-crab Petrolisthes elongatus is extremely common, hiding among the tunicate clusters.

On rocks among the tunicates are many animals and plants. The globose sponge Tethya, and an encrusting bright-orange species, are common. Corallina officinalis is abundant, and collects a lot of mud. It appears to be the most favoured resort of Cerithidea subcarinata. The larger gasteropods include Turbo smaragdus, with fairly clean shells and eroded spire; Cominella adspersa, a very distinct-looking form with a pronounced shoulder beneath the suture, yellow inside, and usually extensively eroded without; Verconella adusta, fairly clean, though sometimes carrying a few small Elminius. Ostrea corrugata up to 7 cm. in length occurs singly or in small clusters. Patiriella regularis is common, and apparently always of a reddish-brown colour. Mytilus canaliculatus occurs singly in crevices. The shells are usually almost covered with Calpidula crepidula, and occasionally also some Calyptraea novae-zealandiae, Amaurochiton glaucus, and Ischnochiton maorianus.

The under-side of stones is equally as rich as the upper surface. Near the mud-line are Ischnochiton maorianus and Lepidopleurus, iredalei; but where the water circulates freely, though light does not fall direct, there are Cynthia, but no algae, and numerous gasteropods, sponges, compound ascidians, sea-anemones, crabs, pelecypods, Flabelligera lingulata, Nereis arnblyodonta, and other worms of various kinds. (Plate 47, fig. 1.)

Corella Association.

Bay of Islands.—On the rocky coast of Long Beach, under stones where no light penetrates, there is often a rich collection of animals. Some of these may be merely sheltering during the recess of the tide; others, on the contrary, belong to species always found attached to the under-side of

Shelled-animals Formation.

Pelecypod Subformation.

In the northern portion of New Zealand, north of S. lat. 38°, Ostrea cucullata forms a conspicuous association in the mid-tide belt. It chiefly affects sheltered coasts, and sometimes covers the rock-surface to a depth of 5 cm. On the other hand, the association of Mytilus in the tidal belt is best developed in the southern portion of New Zealand, especially in the low-tide belt. Modtolus, an ally of Mytilus, occurs near high-tide mark throughout New Zealand.

Similar associations are represented in other temperate regions. In New South Wales (Hedley, 1915, p. 73) and in Queensland Ostrea cucullata is a feature of the shore as conspicuous as it is in New Zealand; but, as the animals occurring with it differ, it would form a distinct subassociation. In the Fiji Group I have noticed an association of a small species of Ostrea. In the British Isles Mytilus edulis is a dominant form, whilst representing the Mytilus association in New South Wales is that, of Brachyodontes hirsutus (Hedley, p. 74), and in Tasmania Mytilus planulatus.

MytilusAssociation.

Taylor's Mistake.—On rocks near low-tide mark there are extensive patches of Mytilus canaliculatus with their shells closely crowded. A large part of the surface of the shell is sometimes deeply eroded. Among the Mytilus are a number of brown and red algae and a little Ulva, whilst the rock-surface itself is covered with pink Melobesia. Many specimens of Mytilus candliculatus contain the crab Pinnotheres pisum. Scattered about the rocks are several species of large molluscs and other animals—Plaxiphora obtecta (clean but eroded), P. biramosa with Melobesia on the valves, Cellana radians, Stichaster suteri, Haustrum haustrum, Turbo smaragdus, and Plaxiphora caelata entirely covered with a short brown alga.

Immediately above the belt of Mytilus canaliculatus, M. planulatus becomes the dominant species. There are here very few algae, and the mollusca and other animals differ in the main from those associated with M. canaliculatus. The most common species are Elminius plicatus, E. modestus, Monodonta aethiops, Cellana radians, Sypharochiton pellisserpentis, Vermilia carinifera (in patches), Brachyodontes maorianus, and, on the valves of M. planulatus, Notoacmea parviconoidea. Here and there clusters of Elminius plicatus also occur on the valves of Mytilus planulatus. (Plate 45, fig. 2.)

OstreaAssociation.

Takapuna.—Ostrea cucullata here occupies a well-defined belt about 1 m. in vertical width, and centred about half-tide mark. The Ostrea shells may be thickly scattered about, they may be in dense clusters, or the entire surface for many square metres may be covered to a depth of 6 cm. to 10 cm. The left valve is deeper than the right, and is attached to the rock by about half its area, the outer margin bending sharply up from the rock-surface as a deeply corrugated cup closed by the less concave right valve. Clusters broken off the rock are found to be composed of many shells firmly joined together. A common arrangement is for the shells to be united in pairs the edges of which partly overlap adjacent shells, thus forming a double fan. But more frequently the clusters are quite irregularly arranged.

When the Ostrea is dense not many other animals are associated with it. The following, however, are found in the locality here described:

Lepsiella scobina, Nerita melanotragus, Turbo smaragdus, Sypharochiton pellisserpentis, Monodonta aethiops, Elminius phcatus, Cellana radians, C. ornatus—all species of wide distribution in the intertidal belt throughout New Zealand. Where the Ostrea forms a complete covering to the rocks only small examples of these animals are found. (Plate 48, fig. 1; Plate 4=6, fig. 2.)

Modiolus Association.

St. Clair.—This association occupies the middle portion of the intertidal belt. The rocks are large hard lava boulders, and the patches of Modiolus pulex are the most conspicuous feature of the beach. The shells grow close together, the umbonal end, near which is the byssus, touching the rock, the anterior end pointing outwards. They harbour a good deal of sand, in which are found many polychaet worms. On the sliells of Modiolus are found Notoacmea parviconoidea, young Melaraphe cincta, and Risellopsis varia; also here and there are bunches of Porphyra columbina. Pelecypods associated with Modiolus are a few Mytilus planulatus and Brachyodontes maorianus. On the rocks where not occupied by Modiolus are a number of mollusca, the following being common: Cellana strigilis, C. radians, Siphonaria obliquata, S. zealandica, Lepsiella scobina, Neothais lacunosa, Plaxiphora caelata (30 mm. in length and covered with small algae), and Monodonta coracina. In rock-pools Modiolus does not occur. Like many animals accustomed daily to be left dry by the tide, it seems to flourish best on rocks not constantly submerged.

Taylor's Mistake.—Near high-water mark is a well-defined belt of rocks almost entirely covered with Modiolus pulex and Elminius modestus. High neap tides cover all the animals in this association except a few Modiolus, Cellana radians, and Monodonta aethiops, but these are reached by the wash of every wave. Associated with the Modiolus and Elminius are Lepsiella scobina, Sypharochiton pellisserpentis, Risellopsis varia, Melaraphe unifasdata, Cellana ornata, C. radians, and Melaraphe cincta. Notoacmea parviconoidea is common on the shells of Modiolus pulex. All these species except Risellopsis and Melaraphe contained water within their shells, and in a specimen each of Cellana and Monodonta was found a small amphipod. At one point in the coast-line at Taylor's Mistake the variety rutila is freely mixed with Lepsiella scobina. There is no apparent difference in the habitat to cause a variation of this kind.

Modiolus confusus Association.

In brackish water Modiolus confusus takes the place of M. pulex in the tidal belt. Unfortunately I have few notes on this association. At Spirits Bay a small river runs into the sea, and is for a portion of its lower course tidal. Here in the brackish water are a few molluscs. Where there is a hard surface Modiolus confusus occurs in clusters. The shells are smooth, not at all eroded, and mesure up to 30 mm. in length. Common on the botton are two species of gasteropoda—Melanopsis trifasciata and Potamopyrgus corolla salleana.

At Riverhead, on the Waitemata River, intertidal rocks support Modiolus confusus (32 mm.) and Elminius modestus; while at Warkworth, on the Mahurangi River, I collected M. confusus and Potamopyrgus antipodum. There appears to be a curious mixture on the western shore of the Great Lagoon on Chatham Island. Here I gathered Modiolus confusus (22 mm.), Antigona stutehburyi (small shells, 25 mm., with convex but not ventricose valves), and Potampyrgus antipodum.

Tubicolous-polychaet Subformation.

There appear to be several associations of this subformation, but I have notes on only one, which, however, occurs in two distinct sub-associations. (Plate 45, fig. 2, and Plate 48, fig. 2.) The association in Auckland Harbour presents little similarity to that on an exposed coast; such as on Tarakihi Rock, except that the dominant species is the same. A different association is that of a worm, Hermella spinulosa, forming large colonies of sand-tubes along the coast in Hauraki Gulf. In Australia the Galeolaria caespitosa association would belong to the present subformation (see Hedley, 1915, p. 64).

VermiliaAssociation.

Auckland Harbour.—This association is found chiefly on the outer portion of the reef of volcanic rocks stretching across the mud-flats from Auckland towards Kauri Point. Here in a low-lying part most of the rock is covered with mud. To the exposed pieces of the reef, and on detached rocks lying about, the colonies of Vermilia carinifera are attached. The Vermilia grows in masses, with the tubes close together and radiating outwards from the point of attachment to the rock. The apertures are all pointing outwards, and the whole mass thus formed may be 1 m. or more in length and½ m. high. The general surface is more or less rounded, and from a distance presents very much the appearance of the vegetable sheep (Raoulia) of the Southern Alps.

Only the ends of the tubes are occupied, each animal being from 3 cm. to 5 cm. in length. The spaces between the tubes are filled with mud. The main portion of the mass is therefore empty tubes and mud. This association is left dry by the tide for a long time each day, and the animals, to protect themselves against desiccation, withdraw into the tubes and close the apertures by shelly opercula. (Plate 48, fig. 2.)

Tarahihi Rock, Hauraki Gulf.—Vermilia carinifera is here the dominant organism in a belt of rocks above the brown-algae formation. Its massed tubes form continuous coverings over large patches of rock. Associated with it is small Chamaesipho columna. There occur also clusters of large specimens of Mytilus canaliculatus (with their shells covered with Vermilia), Chamaesipho, algae, and Crepidula crepidula. Many of the Mytilus shells contain the crab Pinnotheres pisum. Common molluscs on the rocks are the usual intertidal species—Neothais succincta, Lepsiella seobina, Cellana radians, Sypharochiton pellisserpentis, and Monodonta aethiops.

Sessile-cirripede Subformation.(Plate 46, fig. 1.)

This is the most common shelled-animals community in the littoral belt. At every point on the coast some of the intertidal space is occupied by associations in which Elminius or Chamaesipho is dominant. In other temperate regions it appears to be equally well represented. In the British Isles it is Balanus balanoides that is dominant (Southern, p. 24); in Australia and Tasmania species of Balanus, Tetraclita, and Catophragmus. So far as my observations go, this formation, is poorly represented in the tropics: this perhaps is due to excessive insolation.

Elminius plicatus Association.

Takapuna.—At Red Bluff, above the belt of Ostrea cucullata, there is a well-defined belt covered almost entirely with the large Elminius

plicatus. It grows in masses on all the ridges of the irregular rock-surface, avoiding little holes where water can lie; it also avoids the underside of overhanging rocks where Ostrea cucullata, small Chamaesipho columna, and Vennilia carinifera are found. Examining the clusters of Elrmnius closely, it is found that they appear to branch like certain corals; but in reality the branches have no organic connection with the main stem—it is merely a case of young animals settling on the shells of older ones. There may be three, four, or more generations in a cluster, and the average height of the community is between 2 cm. and 3 cm. Various small animals are found on the Elminius shells—Chamaesipho columna, Sypharochiton pellisserpentis, Plaxiphora caelata, small Ostrea cucullata, and Cellana ornata; also a small black alga. There are very few animals on the rock-surface among the Elminius. Cellana ornata, Lepsiella scobina, Haustrum haustrum, and Sypharochiton pellisserpentis were seen, but these are more common in shady places where Elminius plicatus is less abundant.

Otago Peninsula.—At Maori Papanui Bay there is an association of Elminius plicatus covering a wide area of rocks, here chiefly large volcanic boulders, in the mid-tide belt. Algae present are Splachnidium rugosum along the lower margin, and a few patches of Bostrychia arbuscula higher up. The rocks are to a large extent covered with Elminius plicatus. By, young shells growing on the older ones irregular clusters are formed, and when this begins on a shell of Mytilus planulatus the cluster of cirripedes is frequently larger than the mussel which supports it. (Plate 42, fig. 4.) Mytilus planulatus occurs in large patches of closely packed shells, which, as just stated, support clusters of Elminius phcatus, as well as large numbers of Notoacmea parviconoidea, and fewer of Lepstella scobina. Associated with Elminius plicatus on the rocks are Cellana radians, Lepsiella scobina, Notoacmea parviconoidea, and Monodonta aethops. Along the lower edge are found in addition Mytilus canaliculatus, Brachyodontes maorianus, Sypharochiton sinclairi, Neothais striata, and Scalpellum villosum.

Elminius modestus Association.

Stewart Island.—At Half-moon Bay, above the brown-algae formation, the rocks are sprinkled with small Elminius modestus, among which Cellana strigilis, C. radians, and Monodonta aethiops are the most conspicuous shells. The upper portion of this association contains the greatest variety of species. Elminius modestus is still dominant, but there also occurs plentifully a larger species, E. plicatus; also Mytilus planulatus, Brachyodontes maorianus, and Cellana ornata. Patches of Bostrychia arbuscula extend into this association. Other molluscs occurring on the rocks are Sypharochiton pellisserpentis, Plaxiphora terminalis, Siphonaria zealandica, and Lepsiella scobina.

A large assemblage of animals found under stones should perhaps be referred to a separate association, since, though some are animals of the Elminius association merely sheltering, others are permanent residents, not exposing themselves to the drying conditions of the upper surface of the rock. Besides numerous sponges, tunicates, polyzoa, and sipun-culids, there are the following molluscs, echinoderms, and worms: Euthria linea (varying in one direction to E. flavescens and in another to E. vittata),Neothais lacunosa squamatus, Monodonta lugubris, M. atrovirens, Saxicava arctica, Nucula nitidula, Paphia intermedia, Onithachiton negelctus, Patiriella regularis, Stichaster polyplax, Atalacmea unguis-almae, Eulalia microphylla, Nicolea gracilibranchis, and Physcosoma scolops.

Notoacmea pileopsis up to 28 mm. in length, and 14 mm. in height occurs. The apexes of all the shells except those of Notoacmea pileosis and young Nerita melanotragus are eroded. N. pileopsis shows more signs of wear than erosion. A conspicuous feature of the rocks in this association (in April) are tufts of Porphyra columbina.

Under stones in this belt are a few molluscs, including some not able to tolerate drying conditions of exposed rocks. Monodonta lugubris, Sypharochiton pellisserpenlis, and Atalacmea unguis-almae, all with clean uneroded shells, are common. Onchidella is also found here.

Gasteropod Subformation.

Perhaps on account of the mobility of its dominant life-forms, this sub-formation occurs highest on rocks in the intertidal belt. There are two principal growth-forms—gasteropod, with spiral shell, continuous peristome, and close-fitting operculum, and associated with this in all situations except dry rocks above high-tide mark, where Melaraphe alone reigns, the limpet-like growth-form. Several associations may be distinguished.

This subformation is probably represented in all seas. I need only mention the associations of Patella and Littorina on the British coasts, of Nerita and Tectarius in the tropics, and of Cellana and Melaraphe in Australia.

Cellana-MonodontaAssociation.

Otago Harbour.—Rocks between tides at Portobello support a fairly typical harbour-community of shelled animals. The substratum consists of rather soft and easily weathered volcanic clay with a very irregular surface. It easily forms mud, hence the water is frequently turbid and the species consequently few. The shells also are in almost every case eroded, those of Melaraphe cincta and Amaurochiton glaucus being the most resistant. Most of the species are common throughout the association, and attain a large size.

Along the upper limit Melaraphe cincta (18 mm.), with clean non-eroded shells, is common. Here are a few patches of Bostrychia arbuscula. Below there follows the main collection, consisting of Monodonta aethiops (alt. 30 mm.), M. corrosa, Sypharochiton pellisserpentis, Siphonaria zealandica (25 mm.), S. obliquata (young), Cellana ornata, Risellopsis varia (diam. 8 mm.), Patelloidea Stella corticata, and, on the larger shells, Notoacmea daedala. Along the lower edge of the association Cantharidus tenebrosus huttoni (alt. 14 mm.) is abundant. Other animals occurring on the rocks in fewer numbers are Plaxiphora caelata, Ostrea angasi, Onchidella, Cominella lurida, and Euthria linea. A little Corallina officinalis is found in rock-pools, whilst under stones occur Amaurochiton glaucus (always of a dark-green colour). Notoacmea pileopsis, and N. daedala.

Cellana-MelarapheAssociation.

Shag Point.—Of the associations included under the gasteropod sub-formation the present is the richest that I have examined, both in number of species and in individuals. The size of the shells, too, is in most cases very large for the species. There is at Shag Point a wide intertidal shelf. The rock is not hard, being a yellowish sandstone containing many channels connected with the sea at low-tide, and higher up occasional pools, usually the result of the breaking-up of septarian boulders. The inner and upper

portion of this intertidal platform contains a remarkable collection of patelloid molluscs associated with immense numbers of Melaraphe of two species. All the crevices and water-channels are filled with molluscs. Three species of Cellana are almost equally common and mixed together, though they segregate to a certain extent. The shells are not badly eroded, though the apexes of the larger examples are seldom perfect. C. strigilis attains a length of 67 mm., C. radians of 51 mm., and C. ornata 47 mm. With these are associated equally plentifully Siphonaria obliquata (65 mm.), Sypharochiton pellisserpentis, and Siphonaria zealandica (23 mm.). S. obliquata occurs in clusters of fifteen to thirty, the shells often overlapping, on rocks fringing pools. Under water on the bottoms and sides of pools they deposit their ribbon-like spawn in large numbers. Each takes the form of a spiral of two to four turns, and of a diameter of 3 cm. to 4 cm. These spawns are frequently so crowded as to be touching. The spawns of S. zealandica are in the form of crescents, and are deposited in pools, often along with that of S. obliquata. Melaraphe unifasciata and M. cincta occur in immense numbers, sometimes densely clustered together. High up on the rocks Notoacmea pileopsis (26mm.) occurs with M. cincta (20mm.). Shells of N. pileopsis are perfect, but those of M. cincta are widely and often deeply eroded. Other molluscs, collected chiefly under stones, were Monodonta nigerrima, M. coracina (diam. 16 mm.), M. lugubris, and Notoacmea daedala; while N. parviconoidea was found on the rocks. Piles of seaweed are washed up everywhere, and emit a considerable smell. On Macrocystis so cast up Monodonta nigerrima, occurs in incredible numbers, some with shells perfect, others with the black outer layer almost entirely removed, showing the nacreous layer below. Algae take but a small part in the Cellana-Melaraphe association. A Corallina with whitish fronds in some of the pools, and small tufts of Ulva on the rocks, were all that were noticed.

Cellana-NeritaAssociation.

Little Barrier Island.—The rocks here are for the most part large lava boulders. At one point the breccia of the cliffs is hard and compact enough to withstand the surf, and here the association is perhaps best developed. The dominant species are Cellana radians (4.0 mm., alt. 10 mm.) and Nerita melanotragus. With these are associated commonly Monodonta aethiops, M. atrovirens (diam. 27 mm.), Turbo smaragdus, Sypharochiton pellisserpentis, and, at a higher level, Melaraphe unifasciata and Chamaesipho colunvna. Conspicuous patches of the crustaceous brown alga Leathesia occur plentifully on rocks and on shells of Cellana radians. There also occur on Sypharochiton, and on the rocks, Cauldcanthus spinellus and a filiform brown alga. The molluscs, which occur chiefly in the upper portion of the association where it is developed on the breccia cliffs, are Cellana ornata (33 mm., alt. 14 mm.), Siphonaria zealandica, Notoacmea pileopsis (22 mm.), N. septiformis, N. parviconoidea, and Patelloida stella corticata. Under stones occur Atalacmea unguis-almae, Monodonla lngubris, and Actinia tenebrosa.

MelarapheAssociation.

Maori Papanui Bay, Otago Peninsula.—The rock here is hard volcanic, and, as elsewhere, Melaraphe, reaches highest above tide-marks. Only one species, M. cincta, was collected. Both young and adult occur, all with the spire of the shell more or less eroded. Adult shells are elongated; the largest measured 11 mm. Associated with Melaraphe, but not reaching

Burbowing-animals Formation.

on exposed sandy beaches there is one of A. ventricosa in certain parts of the west coast, but I have no details. A different association is found on more sheltered beaches-as, for instance, Dosinia-Tellina in Eangitoto Channel. On mud-flats the presence of Cerithidea bicarinata in the north, and its absence in the south, defines distinct subassociations of the Antigona association.

Hedley describes associations on sand and mud in New South Wales. The Donax deltoides association on sandy beaches may be compared with the Amphidesma subtriangulata association in New Zealand, while Pyrazus herculeus on mud seems comparable with Ce [ unclear: ] rithidea bicarinata. Southern, in his description of Clare Island, does not indicate the dominant species, and I have seen only an extract of Davenport's account of Cold Spring Harbour. Probably a formation of similar structure to that of the burrowing-animals formation here described occurs on intertidal mud and sand in all parts of the world.

Amphidesma. Association.

Tauranga.—At Maunganui Beach there is, exposed to the ocean between tides, a wide stretch of nearly level sand. The whole of the life here appears to be burrowing-animals, pelecypods being dominant. With them are associated some large gasteropods and various crustaceans.

In certain areas Amphidesma subtriangulata occurs in immense nuimbers. In April all the specimens gathered were small—45 mm. and under. They remain just below the surface, in a vertical position. Sometimes after a scour many thousands of shells may be seen partly exposed. The shells are clean, with the periostracum rubbed off around the umbones. Next in order of abundance to Amphidesma is Antigona spissa, occurring just beneath the surface of the sand. The shells are clean, variously coloured, and up to 30 mm. in length. Large gasteropods found in this association are Struthiolaria papulosa, Verconella mandanna, and Cominella adspersa. Verconella has clean uneroded shells, 130 mm. m length, and is found burrowing in sand near rocks. One shell had been severely attacked by burrowing-animals, which had removed a large portion of tee outer layers; untouched parts were scarcely eroded at all. The Cominellae are clean, with the colour-pattern clearly marked, and the surface with more the appearance of having been worn than eroded. Shells gathered have a length up to 52 mm., and the shoulder not well marked. Crustacea include the swimming - crab (Platyonischus bipustulalus), hermit - crabs (Eupagurus novae-zealandiae—plentiful near the rocky coast), and a small isopod which runs quickly across the sand.

Monodonta excavata is found attached to smooth stones, usually at or just below the surface of the sand. The base of the shell is concave, and the periphery of the body-whorl angled. This may be related to the animal's habit of pushing its way beneath the sand covering the base of the rocks. Obviously, too, a larger amount of water can be held in the excavated base than in the body-whorl alone.(Plate 49, fig. 1.)

Dosinia-Tellina Association.

Rangzioto Channel.—At Cheltenham Beach the whole bay between the heads is laid bare at low tide. The surface is clean sand, but at a distance averaging 5 cm. below it is black. The biotic community consists of burrowing-worms, brittle-stars, and pelecypods beneath the surface, with sand-dwelling gasteropods, crabs, and starfishes above.

Burrowing deepest into the sand are Nephthys macrura and other worms. With them, though rare, are brittle-stars belonging to a long-armed species like Amphiura aster. They remain with their body some 10 cm. below the surface, but the tips of their arms project and sweep about in search of food. The large pelecypod Pinna zealandica is (1915) found in fair numbers near low-tide mark. The shells are 20–22 cm. in length, and stand vertically in the sand with only 1–2 cm. of the broad posterior end projecting above the surface. The byssus, which leaves the shell near the buried anterior end, spreads out, and at the end of each thread is attached a grain of sand. This holds as fast as if attached to a fixed object, for if the shell be forcibly taken from its position the byssus invariably breaks at its origin in the foot of the animal. The exposed ends of the shell support a little algae. Eliminius modestus, and worm-tubes. A crab lives commensally within the Pinna shell. Occurring more generally over the flat and just below the surface of the sand are Dosinia subrosea (some with shells stained black), Tellina liliana (68 mm. in length and under), Myodora striata (common near low-tide mark), Antigona stutchburyi (common inshore, where it is said to have been planted), and Amphidesma novae-zealandiae. Less commonly found living here are Callanaitis yatei, Mactra ovata, and Soletellina nitida. All the pelecypods are clean and little eroded.

Gasteropoda occurring in this association belong to two groups—firstly, the sand-dwelling species proper, including Alcithoe arabica, Struthiolaria papulosa, Ancilla australis, and occasionally Calliostoma pellucidum; and, secondly, the carnivorous Cominella adspersa, which occurs also on rocky shores. Alcithoe and Struthiolaria are found near low-tide mark, where they plough their way along just below the surface. Ancilla occurs more generally over the flat, and, like the others, moves beneath the sand. The shells of these species are fairly clean and but little eroded. Living beneath the sand, they remain in moist conditions during the retirement of the tide; and it is perhaps significant in this connection that the operculum is rudimentary in all of them. Cominella adspersa moves along the surface or occasionally just below it, preying on pelecypods, especially Myodora striata. Its shells are usually covered with slime and minute algae, and occasionally there may be some small Elminius.

Hermit-crabs (Eupagiius novae -zealandiae) are common on the mud-flat, occupying gasteropod shells mainly belonging to species inhabiting the adjacent coast. Starfishes—Paliriella regularis and Asterias calamaria—roam about near low-tide mark. Occasionally the curious Callianassa filholi is found.

Antigona Association.

Tauranga.—Sandy mud, black a little way beneath the surface, perhaps describes best the extensive flats not occupied by Zostera between tide-marks in Tauranga Harbour. Two strata of life are represented: the subsurface fauna consists of burrowing-crabs, worms, and pelecypods; on the surface are gasteropods, both vegetable-feeders and predacious kinds, supporting on their shells a few small animals of the tent-like form. A button-like alga is found here and there, usually near low-tide mark, where is is associated with a sponge and a small brown alga.

The flats are riddled with the burrows of the crabs Heterograpsus crenulatus and Hemiplax hirlipes. In making their burrows they bring up quantities of black sand, which makes the entrances conspicuous. Just beneath the surface Antigona strutchburyi abounds. The shells are usually

small, with high concentric ribs, and with the posterior end often eroded, stained, or attacked by a borer. Tellina liliana occurs in fewer numbers.

Scattered thickly over the surface of the mud are Cerithidea bicarinata and Cominella lurida. The latter animal is carnivorous, and is often found congregated in large numbers round its prey. I counted forty-two clustered round a dead crab, and seventy-five round a Tellina. Antigona frequently falls a prey to this mollusc. The whole outer surface of the shells of Cominella lurida is generally eroded and stained. The upper spire-whorls of Cerithidea bicarinala are always eroded. Monodonta subrostrata is usually found on stones lying about the mud. Cominella adspersa, C. maculosa, and Turbo smaragdus occur commonly, all with the spire more or less eroded. In certain places, usually near high-tide mark, Amphibola crenata is abundant. The shells of the species, though often stained; are very successful in resisting erosion. The protoconch may frequently be recognized in adult shells. Among animals habitually attached to the shells of the larger molluscs are sea-anemones, on the posterior end of Antigona shells; Crepidula crepidula, on Turbo smaragdus; small Amaurochiton glaucus, Elminius modestus, and Notoacmea parviconoidea, on Turbo and Amphibola.

Parenga Harbour.—Mud-flats between tides where not covered by Zostera are occupied below the surface by crabs, Helice crassa, and a few Antigona stutchburyi. The shells of this species here measure as much as 40 mm. in length, whilst in the adjacent Zostera beds the usual size is about half this. On the surface in this association are Amphibola crenata, Cerithidea bicarinata and Cominella lurida. Shells of Cerithidea bicarinata attain a length of 33 mm.; the largest shell gathered on the Zostera beds was 22 mm. long.

Heathcote Estuary.—Mud-flats without Zostera or algae occupy the greater portion of the Heathcote Estuary. Everywhere are crabs' burrows occupied by Helice crassa and Heterograpsus crenulatus. Just beneath the surface of the mud is Antigona stutchburyi, wliile deeper, about 10 cm. from the surface, is found, but less commonly, the larger pelecypod Mactra ovata. Everywhere down to a depth of 10 cm. to 15 cm. are worms of the species Scoloplos cylindrica and Aricia papillosa. On the surface Amphibola crenata is abundant. Equally common are Monodonta corrosa and Cominella lurida, all three species having the shells considerably eroded. On the larger shells there occur small specimens of Notoacmea pileopsis. The banks along the edge of the mud-flats are burrowed into by Helice crassa; under stones on the flat are Heterograpsus crenulatua, Melita inaequis, and the worms Nereis herguelenensis, Nephthys macrura, and Scolecolepides benhami. (Plate 49, fig. 2, Lyttelton Harbour.)

Phytia Association.

Rangitolo.—Among rocks near high-water mark on the south coast of Rangotito there is a good deal of mud, and here is developed an association perhaps related to the mud-flat associations in the same way as Melaraphe and Elminius associations on rocks are related. The animals are tolerant of mud, and can live for more than half their time out of water. Two of the members of this association are pulmonates. Phytia ornata is the dominant form, and is abundant, on mud in shady places and under stones; Marinula filholi is not so common. Other members of this association, which comprises only small specips, are Acmella neozelanica, among green filamentous algae and under stones, and Potamopyrgus

Grass-wrack Formation.

Zoslera beds occur on mud-flats between tides in harbours throughout New Zealand. They extend from about half-tide mark down to below low-water level. They appear to be as equally well developed in Parenga Harbour, near the North Cape, as in Paterson Inlet, Stewart Island. The substratum varies from soft deep black and evil-excelling mud to nearly pure sand. It is only on a few sheltered beaches, however, that Zostera is found in sand, and the patches are always of small extent. Three strata of life are to be distinguished in this formation—a subsurface layer of burrowing pelecypods, crabs, and worms; a surface layer of gasteropods; and the green vegetative portion of the Zostera, with its herbivorous gasteropods. The rhizomes of Zostera are matted, thus giving a firm hold, while the leaves completely cover the surface, which they protect from tidal scouring. The chief feature of Zostera, however, is the ribbon-like form of the leaves, evidently an adaptation to tidal currents. According to Ostenfeld (Rep. Danish Biol. Sta., vol. 16, p. 6, 1908), the leaves contain air, which causes them to stand upright in the water.

There is an extensive literature on Zostera. Here will be noticed that Southern describes an intertidal formation in Clew Bay, west of Ireland, and Hedley gives an account of the Zostera association between tides in Sydney Harbour.

Tauranga.—At Sulphur Point is an extensive area of flats between tide-marks covered with Zostera. The substratum is sandy mud, black immediately below the. surface; the surface is slightly uneven, so that water lies in wide, shallow pools, and the association is consequently, for the most part, quite wet while the tide is out. The rhizomes of Zostera nana, with their roots and leaf-bases, form, just below the surface, a dense mat of vegetation, which effectually holds the mud together. Above the surface their short leaves, 10–15 cm. long, practically cover the ground, which is thus fairly well protected from ihe scour of the tide. Crabs' burrows are common. Descending obliquely for a few centimetres they then extend horizontally. Three species were collected—Heterograpsus crenulatus, Helice crassa, and Hemiplax hirtipes. Antigona stutchburyi is abundant just below the surface, but only small specimens, with shells 23 mm. and under in length, were observed. The posterior portion of the valves was eroded and stained. Nucula hartvigiana appears to be common, also small examples of Tellina liliana.

Molluscs occurring on the surface of the mud are Cominella adspersa, C. maculosa, C. lurida, Cerithidea bicarinata, and small Neothais succincta, all with the shells more or less eroded. On the Zostera leaves are herbivorous, gasteropods—Turbo smaragdus, Monodonta subrostrata, and Canifiaridus tenebrosus huttoni. Certain animals habitually rely on molluscs to carry them about. Sea-anemones attach themselves to the shells of Antigona stutchburyi. Turbo smaragdus here carries large loads: there may be a colony of Vermilia carinifera as bulky as the Turbo shell, or there are found Crepidula crepidula, Notoacmea parviconoidea, or algae containing Dardanula olivacea. The Crepidula itself is sometimes covered with Vermtlia and Spirorbis. Amaurochiton glaucus is found on the larger shells of Cominella adspersa and Neothais succincta.

Among Zostera in shallow pools are shrimps, small crabs, and Haminea zealandica. Also, attached to Zostera leaves and other objects, are two species of a sea-anemone and a small button-like alga. Common in these shallow pools are little clumps of Corallina officinalis entangled with a sponge, on which are found numbers of Cerithidea subcarinata, Dardanula olivacea, turbellarians, and small crabs.

Notoacmea scapha I have found in other parts of Tauranga Harbour not far from Sulphur Point. It was observed only on the leaves of Zostera. The shell is narrow, not wider than the leaf, and about twice as long as broad. It thus differs in shape from all the other New Zealand species of Acmeidae, and the peculiar outline is evidently related to its station. By not projecting beyond the margin of the Zostera leaf it offers the minimum amount of resistance to the action of tide and waves.

Parenga Harbour.—On mud-flats between tides in the most northern harbour in New Zealand are extensive areas covered with Zostera nana. Beneath the surface are many crabs of the species Hemiplax hiritpes; also the pelecypods Antigona stutcliburyi, 20 mm. and under in length, and Nucula hartvigiana. On the surface the following gasteropods are found: Lepsiella scobina, large shells up to 35 mm. in length and with the entire outer surface eroded, and often supporting Vermilia carinifera; Turbo smaragdus, fairly clean shells with eroded apex and carrying Crepidula crepidula and Vermilia carinifera; Cominella lurida, with outer surface entirely eroded; Monodonta subrostrata: Cerithidea bicarinata and C. subcarinata. The chiton Acanthochiton zealandicus also occurs in this association.

Golden Bay, Stewart Island.—Between tide-marks are areas of sandy flats covered with Zostera. Compared with other parts of New Zealand this is a fairly rich association, with large molluscs. Burrowing beneath the surface are Hemiplax hirtipes; Antigona stutchburyi, up to 46 mm. in length, slightly discoloured, low sculpture, and rounded not ventricose valves; Paphia intermedia, 43 mm.; Amphidesma novae-zealandiae, 50 mm., with dark-coloured periostracurn; and Tellina liliana. On the surface there occur Alcithoe arabica elongata, with shells that show a good deal of erosion but are not discoloured, and show also the colour-pattern on the body-whorl. On Zostera leaves are Trophon anibiguus, Monodonta atrovirens, and Gantharidus tenebrosus huttoni.

A feature of the Zostera beds are loose stones lying about. They support Elminius modestus, Mytilus planulatus, Monodonta aethiops, Siphonaria zealandica, Hormosira Banksii, and other small algae. On the under-side are Euthria linea, E. flavescens, Neothais lacunpsa squamatus, Amaurochiton glaziczis, Ischnochiton camphelli, and various worms. These rock-associations are evidently but detached portions of a shelled-animals formation of the adjacent rocky coast.

Salt-reed-swamp Formation.

In many harbours in New Zealand the outer fringe of salt reed swamps is invaded by tidal waters. In such places part of the marine fauna of the adjacent mud-flats is found.

Tauranga Harbour.—Along the landward border of tidal mud-flats considerable stretches of the shore are occupied by salt reed swamp, of which the species occupying the outside edge are Juncus maritimus and Leplocarpus simplex. High tide floods a strip of varying width, and here burrowing in the mud is the crab Helice crassa, and on the surface the gasteropod Amphibola crenata. Farther inland other species of plants enter, and there are often mud lanes lined with Samolus repens

and Selliera radicans. Here also are found the same two species of marine animals. Patches of Scirpus americanus occur out on the flats, with Zostera as an undergrowth. There is also an association of Scirpus americanus, Triglochin striatum, and Paspalum distichum, with Helice crassa, Amphibola crenata, and Potamopyrgus antipodum.

Mangrove Formation.

Mangrove is a formation of woody plants growing in mud between tide-marks, and includes, besides shrubs, a surface and subsurface marine fauna. The animals are similar to those of the adjacent mud-flats, but apparently poorer in species—at least, in the only locality that I examined. Very interesting ecological relations have been described for mangrove, but only two points will be mentioned here. In Avicennia officindlis horizontal roots below the surface of the mud give off many erect peg-like pneumatophores projecting to 30 cm. or so above the mud and functioning as respiratory roots. As a provision for quickly becoming fixed in the mud the embryo before it falls from the tree germinates as far as bursting the seed-coat, providing rudimentary roots and green cotyledons. An account of the New Zealand mangrove has been given by Cockayne (1921, p. 65; also N.Z. Plants and their Story, p. 35, 1919). Further details of the ecology of mangrove formations, with references to literature, will be found in the works of Warming (1909, p. 234) and Schimper (1903, p. 395). Mangrove is found in New Zealand in all tidal estuaries and inlets as far south as Kawhia and Tauranga Harbours. (Plate 50)

Auckland Harbour.—In Shoal Bay the mangrove is small, but all of even height—about 1 m. It covers an extensive area near the level of high tide. The muddy floor is very soft, and therefore badly aerated; but the mangrove makes up for this by its pneumatophores, which rise at close intervals from the subsurface roots. The mud is riddled with burrows occupied by the crab Helice crassa. On the surface is Amphibola crenata, with small shells (25 mm. and under) covered with green slime. Near the land edge of the mangrove, Potamopyrgus antipodum, Phytia ornata, and small amphipods are abundant.

IV. Literature.